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ORNL/TM-2016/298/R1
Exemplary Design Envelope Specification
for Standard Modular Hydropower
Technology
Adam Witt Brennan T. Smith Achilleas Tsakiris Thanos Papanicolaou Kyutae Lee Kevin M. Stewart
et al.
February 2017
Approved for public release. Distribution is unlimited.
DOCUMENT AVAILABILITY
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ORNL/TM-2016/298/R1
Environmental Sciences Division
EXEMPLARY DESIGN ENVELOPE SPECIFICATION FOR
STANDARD MODULAR HYDROPOWER TECHNOLOGY
Oak Ridge National Laboratory
Adam Witt Brennan T. Smith
Kyutae Lee
Scott DeNeale
Jason L. Pries
Kevin M. Stewart
Mark Bevelhimer
Timothy A. Burress
Brenda Pracheil Ryan McManamay
Shelaine Curd
University of Tennessee–Knoxville
Achilleas Tsakiris Thanos Papanicolaou
Kivanc Ekici Benjamin Kutz
Knight Piésold and Co.
Norman Bishop
McKeown and Associates LLC
Alisha R. Fernandez
US Department of Energy
Timothy Welch
Daniel Rabon
Revision 1
Date Published: February 2017
Prepared by
OAK RIDGE NATIONAL LABORATORY
Oak Ridge, TN 37831-6283
managed by
UT-BATTELLE, LLC
for the
US DEPARTMENT OF ENERGY
Contract DE-AC05-00OR22725
iii
CONTENTS
LIST OF FIGURES ...................................................................................................................................... v
LIST OF TABLES ...................................................................................................................................... vii
ABBREVIATIONS, ACRONYMS, AND INITIALISMS ......................................................................... ix
ACKNOWLEDGMENTS ......................................................................................................................... xiii
EXECUTIVE SUMMARY ........................................................................................................................ xv
1. INTRODUCTION .................................................................................................................................... 1
2. EXEMPLARY DESIGN PRINCIPLES AND CONCEPTS .................................................................... 3 2.1 Exemplary Design Principles ..................................................................................................... 5 2.2 Features of Successful Facilities ................................................................................................. 6 2.3 Implementation Through Functional Decomposition ................................................................. 7
APPENDIX A. GENERATION MODULE ............................................................................................. A-1 A.1 Objectives ............................................................................................................................... A-1 A.2 Requirements .......................................................................................................................... A-3 A.3 Inputs, Functional Relationships, and Processes .................................................................... A-7
A.3.1 Necessary Inputs ........................................................................................................ A-7 A.3.2 Functional Relationships ........................................................................................... A-7
A.4 Measures of Performance ..................................................................................................... A-16 A.4.1 Module Unit Efficiency Characteristics .................................................................. A-16 A.4.2 Scalability ................................................................................................................ A-17 A.4.3 Size .......................................................................................................................... A-18 A.4.4 Installed Cost ........................................................................................................... A-19 A.4.5 Estimated Useful Life .............................................................................................. A-20 A.4.6 Maintainability ......................................................................................................... A-20
A.5 Design Constraints ................................................................................................................ A-21 A.6 Design Envelope Specification ............................................................................................. A-22
A.6.1 State-of-the-Art Advances ....................................................................................... A-23 A.6.2 Research Gaps ......................................................................................................... A-26
APPENDIX B. FISH PASSAGE MODULE ............................................................................................ B-1 B.1 Objectives ............................................................................................................................... B-1 B.2 Requirements .......................................................................................................................... B-2 B.3 Inputs, Processes, Functional Relationships ........................................................................... B-8
B.3.1 Necessary Inputs ........................................................................................................ B-9 B.3.2 Functional Relationships ........................................................................................... B-9
B.4 Measures of Module Performance ........................................................................................ B-16 B.5 Design Constraints ................................................................................................................ B-17 B.6 Design Envelope Specification ............................................................................................. B-18
APPENDIX C. SEDIMENT PASSAGE MODULE ................................................................................ C-1 C.1 Objectives ............................................................................................................................... C-1 C.2 Requirements .......................................................................................................................... C-2 C.3 Inputs, Functional Relationships and Processes ..................................................................... C-5
C.3.1 Necessary Inputs ........................................................................................................ C-6 C.3.2 Functional Relationships ........................................................................................... C-6
C.4 Measures of Module Performance ........................................................................................ C-11 C.5 Module Design Constraints .................................................................................................. C-13
iv
C.6 Design Envelope Specification ............................................................................................. C-15
APPENDIX D. RECREATION PASSAGE MODULE ........................................................................... D-1 D.1 Objectives ............................................................................................................................... D-1 D.2 Requirements .......................................................................................................................... D-3 D.3 Inputs, Functional Relationships and Processes ..................................................................... D-5
D.3.1 Necessary Inputs ........................................................................................................ D-5 D.3.2 Functional Relationships ........................................................................................... D-6
D.4 Measures of Performance ..................................................................................................... D-10 D.5 Design Constraints ................................................................................................................ D-12 D.6 Design Envelope Specification ............................................................................................. D-13
D.6.1 State-of-the-Art Advances ....................................................................................... D-14 D.6.2 Research Gaps ......................................................................................................... D-15
APPENDIX E. WATER PASSAGE MODULE ...................................................................................... E-1 E.1 Objectives ............................................................................................................................... E-1 E.2 Requirements .......................................................................................................................... E-2 E.3 Inputs, Functional Relationships and Processes ..................................................................... E-7
E.3.1 Necessary Inputs ........................................................................................................ E-7 E.3.2 Functional Relationships ........................................................................................... E-8
E.4 Measures of Module Performance ........................................................................................ E-12 E.5 Design Constraints ................................................................................................................ E-14 E.6 Design Envelope Specification ............................................................................................. E-15
APPENDIX F. FOUNDATION MODULE ............................................................................................. F-1 F.1 Objectives ............................................................................................................................... F-2 F.2 Requirements .......................................................................................................................... F-3 F.3 inputs, Functional Relationships, and Processes .................................................................... F-7
F.3.1 Necessary Inputs ........................................................................................................ F-7 F.3.2 Functional Relationships ........................................................................................... F-8
F.4 Measures of Performance ....................................................................................................... F-8 F.5 Constraints ............................................................................................................................ F-10 F.6 Design Envelope Specification ............................................................................................. F-11
APPENDIX G. TERMINOLOGY ............................................................................................................ G-1
APPENDIX H. REFERENCES ................................................................................................................ H-1
v
LIST OF FIGURES
Figure 1. Conceptual schematic of an SMH facility and constituent modules as “black boxes.” ................ 2 Figure 2. Hierarchical structure of natural stream environments and hydropower systems. ........................ 4 Figure 3. Conceptual schematic of the specific objectives of a generation module. ................................ A-2 Figure 4. Specific objectives from Figure 3 mapped on a conventional run-of-river hydropower
facility. .............................................................................................................................................. A-3 Figure 5. Example flow duration curve with important flow design parameters. ................................... A-10 Figure 6. A hill chart documenting the hydraulic efficiency (shown as labeled contours) of a
water turbine at various head and flow combinations. .................................................................... A-12 Figure 7. Optimum runner blade geometry for a given specific speed. .................................................. A-13 Figure 8. Idealized generator system power-speed characteristics for wide speed range operation. ...... A-14 Figure 9. Turbine efficiency for different turbine types at constant speed as a function of
percentage of full load. .................................................................................................................... A-16 Figure 10. Example of the performance improvement expected from variable-speed turbines with
adjustable gates. .............................................................................................................................. A-17 Figure 11. Single runner diameter for small, low-head (<10m) conventional hydropower turbines
(bulb Kaplan, vertical Kaplan, Francis) and embedded generator designs (Amjet, VLH,
StreamDiver). .................................................................................................................................. A-19 Figure 12. Project cost estimates for new stream-reach hydropower developments in the United
States provided during the planning, engineering, and construction phases of project
development. ................................................................................................................................... A-20 Figure 13. Average power output of the new VSD and PMG system compared with the former
induction generator.......................................................................................................................... A-24 Figure 14. Net real power efficiency of the new VSD and PMG system compared with the
former induction generator. ............................................................................................................. A-24 Figure 15. Amjet Turbine Systems low-head turbine with embedded permanent magnet generator
and variable-speed electronic flow control that eliminates the need for conventional
peripheral equipment. ...................................................................................................................... A-25 Figure 16. VLH turbine technology (right) eliminates powerhouse superstructure associated with
more conventional technologies (left). ............................................................................................ A-26 Figure 17. Installed unit (left) and cutaway sketch (right) of the Turbinator turbine-generator
integrated technology installed without a powerhouse. .................................................................. A-26 Figure 18. Conceptual schematic of the specific objectives of a fish passage module. ............................ B-2 Figure 19. Swimming speeds for various species of fish: (left) adult individuals, (right) juvenile
individuals. ...................................................................................................................................... B-10 Figure 20. Fish endurance (vertical axis) as function of fish swimming speed (horizontal axis) for
different fish species and water temperatures (after Ficke et al. 2011). .......................................... B-11 Figure 21. Relationship between the flow discharge, bed slope, and flow depth (Katopodis 1992). ..... B-13 Figure 22. Geometries of different fish passage modules and the expected flow patterns. .................... B-13 Figure 23. Relationship between the flow velocity (vertical axis) and discharge (horizontal axis)
in the fish passage module (Katopodis 1992). ................................................................................ B-14 Figure 24. Flow patterns in fish passage modules of different geometry. .............................................. B-15 Figure 25. Conceptual schematic of the specific objectives of a sediment passage module. ................... C-2 Figure 26. Correlation of the bedload transport rate (vertical axis) with the excess bed shear
stress (horizontal axis)....................................................................................................................... C-8 Figure 27. Critical shear stress as a function of the grain Reynolds number for different degrees of
grain protrusion, denoted as (p/D), in relation to the flow and different grain shapes. ..................... C-9 Figure 28. Percentage of sediment transported as bed load and suspended load as a function of
the ratio of sediment fall velocity to friction velocity. ...................................................................... C-9
vi
Figure 29. Relationship of suspended sediment load (vertical axis) to the flow discharge and
watershed steepness (horizontal axis). ............................................................................................ C-10 Figure 30. Threshold values of (a) the index for sediment aggradation and degradation and (b) the
index of incision potential for various hydropower facilities.......................................................... C-12 Figure 31. Threshold values of (a) the index for flood magnitude reduction and (b) the index of
incision potential for various hydropower facilities. ....................................................................... C-12 Figure 32. Thresholds of the morphologic change indices of Grant et al. (2003) where the effects
of hydropower facilities on river morphology are subtle. ............................................................... C-13 Figure 33. Conceptual schematic of the specific objectives of a recreation passage module. .................. D-2 Figure 34. Hydraulic jump behavior at an abrupt drop. ............................................................................ D-7 Figure 35. Prediction of hydraulic jump type. .......................................................................................... D-8 Figure 36. Inlet control structure designed with a slotted apron that creates an undular hydraulic
jump with no recirculation. ............................................................................................................... D-9 Figure 37. Whitewater classification versus slope and flow. .................................................................... D-9 Figure 38. Empirical prediction of hydraulic jump type. ........................................................................ D-11 Figure 39. Suggested depth and velocity criteria for canoeing and kayaking. ........................................ D-11 Figure 40. Combined canoe and fish pass in the United Kingdom. ........................................................ D-14 Figure 41. Canoe/kayak slide adjacent to a fish passage structure located at a gated weir. ................... D-15 Figure 42. Conceptual schematic of the specific objectives of a water passage module. ......................... E-2 Figure 43. Dependence of the bankfull discharge on the watershed drainage area for different
hydrologic units in New York state. (Mulvihill and Baldigo 2012) ................................................. E-9 Figure 44. (a) Example of a typical hydrograph indicating the flow response (blue curve) to
precipitation (gray bars). ................................................................................................................. E-10 Figure 45. Relationship between the weir discharge coefficient (vertical axis) and the available
water head (horizontal axis) for an ogee-shaped weir. (USBR 1977) ............................................. E-11 Figure 46. Conceptual schematic of the imposed loads a foundation module must resist. ....................... F-2 Figure 47. Conceptual schematic of the environmental mechanics a foundation module must
resist. ................................................................................................................................................. F-3
vii
LIST OF TABLES
Table 1. Generation module requirements. ............................................................................................... A-4 Table 2. Necessary inputs for generation module design ......................................................................... A-7 Table 3. Functional relationships governing the generation module operation ........................................ A-7 Table 4. US hydrologic classification (McManamay et al. 2013) .......................................................... A-11 Table 5. GM design constraints .............................................................................................................. A-21 Table 6. Classification of barriers with respect to fish movement (adapted from the California
Department of Fish and Game) ................................................................................................ B-1 Table 7. Fish passage module functional requirements: objective 1—attract fish to the module. ............ B-4 Table 8. Fish passage module functional requirements: objective 2—allow fish to cross SMH
facility. ..................................................................................................................................... B-6 Table 9. Fish passage module functional requirements; objective 3—allow fish to exit safely into the
stream. ...................................................................................................................................... B-8 Table 10. Key inputs for the function of the fish passage module ............................................................ B-9 Table 11. Functional relationships governing fish passage module operation ......................................... B-9 Table 12. Key physiological characteristics for common freshwater fish species (Meixler et al.
2009). ..................................................................................................................................... B-12 Table 13. Measures of fish passage module performance ...................................................................... B-16 Table 14. Fish passage module design constraints.................................................................................. B-17 Table 16. Sediment passage module requirements. .................................................................................. C-3 Table 17. Key inputs for the function of the sediment passage module ................................................... C-6 Table 18. Summary of the key functional relationships relevant to operation of the sediment passage
module ..................................................................................................................................... C-7 Table 19. Sediment passage module measures of performance .............................................................. C-11 Table 20. Sediment passage module design constraints ......................................................................... C-14 Table 21. Recreation passage module requirements. ................................................................................ D-3 Table 22. Recreation passage module necessary inputs for hydraulic design .......................................... D-5 Table 23. Summary of key functional relationships necessary for recreation passage module design .... D-6 Table 24. Recreation passage module measures of performance ........................................................... D-10 Table 25. Recreation passage module design constraints ....................................................................... D-12 Table 26. Water passage module requirements......................................................................................... E-3 Table 27. Water passage module functional requirements. ...................................................................... E-5 Table 28. Water passage module functional requirements. ...................................................................... E-6 Table 29. Water passage module necessary inputs ................................................................................... E-8 Table 30. Functional relationships governing water passage module operation ....................................... E-8 Table 31. Water passage module measures of performance ................................................................... E-13 Table 32. Water passage module design constraints ............................................................................... E-14 Table 33. Foundation module requirements. In the fourth column: F = Functional; P = Performance;
I = Interaction; O = other. In columns 6–11, an “X” denotes a relationship to the river
continuum constituent indicated in the top row ...................................................................... F-3 Table 34. Foundation module necessary inputs for module design .......................................................... F-7 Table 35. Functional relationships governing foundation module operation ............................................ F-8 Table 36. Foundation module measures of performance .......................................................................... F-9 Table 37. Foundation module design constraints .................................................................................... F-10
ix
ABBREVIATIONS, ACRONYMS, AND INITIALISMS
AC alternating current
cfs cubic feet per second
DC direct current
EDES Exemplary Design Envelope Specification
EDF energy dissipation function
FM foundation module
GM generation module
IHA Indicators of Hydrologic Alteration
MYRP Multi-Year Research Plan
PM passage module
PMG permanent magnet generator
R&D research and development
SMH standard modular hydropower
TKE turbulent kinetic energy
VSD variable-speed drive
xiii
ACKNOWLEDGMENTS
The authors would like to acknowledge and express their appreciation to all the following individuals and
programs for their review, comments, and support of this report and support of Standard Modular
Hydropower research efforts.
Oak Ridge National Laboratory
Deborah Counce, Technical Writer/Editor
Kathy Jones, Electronic Media Specialist
Rose Raney, Technical Writer/Editor
Priscilla Henson, Publications Manager
Andy Sproles, Graphic Artist
Dami Rich, Graphic Artist
Douglas Edwardson, Web Developer
Shih-Chieh Kao, Statistical Hydrologist
Nicole Samu, Geospatial Data Coordinator/Cartographer
Christopher DeRolph, GIS Analyst and Aquatic Ecologist
Missy Miller, Administrative Assistant
Greg Zimmerman, Group Leader, Human Health Risk and Environmental Analysis
Patrick O’Connor, Energy Analyst
New Mexico Institute of Mining and Technology
Rebecca Brink, Science Undergraduate Laboratory Intern
University of Minnesota
The authors extend their gratitude to Professor John Gulliver of the Civil, Environmental, and
Geo- Engineering Department at the University of Minnesota for his meaningful insights and
detailed review of this report.
Small Hydropower Stakeholders
The authors would like to thank the many stakeholders with whom we have engaged to elicit
feedback on the opportunities and challenges associated with developing and deploying standard
modular hydropower technologies. Ongoing engagement with these technology innovators,
commercial service/equipment providers, project developers, and environmental stewards has yielded
insight into the myriad perspectives and experiences that shape the current hydropower landscape and
inform standard modular hydropower research.
Copyright Holders
In addition, the authors would like to thank the many publishers, organizations, and individuals who
have granted Oak Ridge National Laboratory permission to reuse various figures, graphics, and
information that aid in communicating and illustrating key research concepts.
xv
EXECUTIVE SUMMARY
Hydropower is an established, affordable renewable energy generation technology supplying nearly 18%
of the electricity consumed globally. A hydropower facility interacts continuously with the surrounding
water resource environment, causing alterations of varying magnitude in the natural flow of water,
energy, fish, sediment, and recreation upstream and downstream. A universal challenge in facility design
is balancing the extraction of useful energy and power system services from a stream with the need to
maintain ecosystem processes and natural environmental function. On one hand, hydroelectric power is a
carbon-free, renewable, and flexible asset to the power system. On the other, the disruption of
longitudinal connectivity and the artificial barrier to aquatic movement created by hydraulic structures
can produce negative impacts that stress fresh water environments. The growing need for carbon-free,
reliable, efficient distributed energy sources suggests there is significant potential for hydropower projects
that can deploy with low installed costs, enhanced ecosystem service offerings, and minimal disruptions
of the stream environment.
The Exemplary Design Envelope Specification (EDES) for Standard Modular Hydropower (SMH)
Technology offers a new paradigm for small hydropower technology development, based on the premise
that standardization, modularity, and preservation of stream functionality must become essential and fully
realized features of next-generation hydropower technologies and project designs. As documented in this
report, a module is an independently deployable and operable unit with explicit objectives, requirements,
and constraints governed by the natural stream environment. A generation module transforms incoming
water flow into an energy output and outgoing water flow. A downstream passage module transfers water,
fish, sediment, or boats safely through a facility. An upstream passage module enables fish to transit
upstream safely. A foundation module provides a stable platform that enables itself and other modules to
maintain location, orientation, and stability. A multiplicity of these modules function in complementary
and coupled ways within a facility to produce energy and minimize disruptions to natural stream
functions.
The EDES provides a framework for technology-neutral conceptual design. It documents the
functionalities that are necessary for successful module operation, independent of how these
functionalities are accomplished. The general structure of this document is the identification of the
objectives, requirements, constraints, and performance of exemplary modules. An effort is made to
identify functional relationships that describe the system and module performance attributes needed to
minimize disruptions of the river continuum. Both state-of-the-art advances and research gaps and
challenges are identified, offering perspective on the evolution of SMH technologies.
This document represents Revision 1 of the SMH Exemplary Design Envelope Specification and will be
updated periodically.
1
1. INTRODUCTION
Hydropower has been a reliable renewable energy generation technology for more than 100 years,
producing valuable energy and non-energy benefits. In that time, the state of the art for facility design and
operation, including generation technology, civil engineering works, and environmental mitigation
technology, has been refined for both large- and small-scale development. As with other critical
infrastructure designs, hydropower design philosophies have emphasized the safety and long-term
reliability of energy production through incremental advancements in technology and process. However,
as the science of complex aquatic, riparian, and terrestrial ecosystems and their vulnerability to
disturbance has been revealed (Trussart et al. 2002; Renöfölt et al. 2010; Poff and Zimmerman 2010; Kao
et al. 2014), new design and operating constraints to protect or restore ecological function have emerged
as essential concepts in the hydropower project development process. So, too, has the inherent worth of
the recreational and aesthetic functions of streams become an important consideration in hydropower
siting and engendered new constraints in project design. As with most design endeavors, the addition of
new constraints to the traditional hydropower design paradigm either increases costs or eliminates sites
from consideration where the totality of constraints cannot be satisfied. In either case, the result is fewer
opportunities for which traditional design paradigms are feasible—this is the challenge faced by
developers of new hydropower projects.
The Exemplary Design Envelope Specification (EDES) presents a new paradigm for small hydropower
technology development based on progressive concepts put forth by hydropower developers (Bishop et al.
2015) and global hydropower consortiums and organizations (IEA 2000; TN SHP 2005; ICPDR 2013).
The Multi-Year Plan for Research, Development, and Prototype Testing of Standard Modular
Hydropower Technology (MYRP; Smith et al. 2016) describes the context for the EDES. Within the
standard modular hydropower (SMH) project, the EDES details the hypothesis that standardization,
modularity, and ecological function as principal design concepts can enable hydropower technology to
deploy and operate with minimal environmental impact and greater public acceptance at reduced costs.
This new design paradigm encompasses more than the hydroelectric powertrain; it calls for
standardization and modularity of every aspect of a hydropower facility so as to enable efficiency of
design, safety review, environmental protection, manufacture, installation, operation, maintenance,
replacement, and removal.
The concept of modularity can be understood in two ways. First, modularity within the facility refers to
the use of different module types to assemble an entire SMH facility. For example, a site may require
several module types:
a generation module that encompasses all hydraulic and electric machines, equipment, and systems
necessary for hydroelectric power generation
passage modules that enable the consistent and predictable passage of fish (upstream and
downstream), sediment, water, and recreational craft
and foundation modules that provide structural resistance and reliably interface with the streambed to
support generation and passage modules
All these modules can be assembled to form an SMH facility that matches the scale, environmental
attributes, and watershed context of the site selected for development. The second concept of modularity
refers to scalability at many sites through multiple modules of the same type. An upstream fish passage
module may be applicable at many sites within a watershed region. A cost-optimized, compact generation
module designed with wide operational flexibility could be applied at multiple sites throughout the
country. This report is a first step toward gaining consensus within the broader hydropower stakeholder
community on how a future based on modularity in hydropower design can be realized.
2
To address the vast range of module specification possibilities, the EDES describes the functionality that
modules and facilities must provide, but not how they provide that functionality. It explicitly specifies the
hydraulic, structural, electrical, and environmental requirements and constraints for physical modules.
The “how” of module design and functionality is the province of the inventor and innovator, and there
may ultimately be many designs that are validated as satisfying design constraints and meet specifications
for functionality (these many designs are the “envelope” in the EDES title). An important requirement
within the specifications is interoperability of modules to enable multiple-module facility design that also
provides the required functionality. Ultimate success in this rigorous design paradigm will be the
acceptance of validated, pre-certified modules for multiple deployments, and a significant reduction in the
burden and uncertainty of site-specific design, safety, and environmental review for all stakeholders.
The goal of this report is to converge on a validated set of objectives, requirements and constraints that
establish a bounded envelope of design for SMH modules. It is critical to note that the EDES does not
propose an ideal design for an SMH facility or for an individual module. The goal is to develop a
technology-agnostic framework in the early design phase and remain uncommitted to specific designs,
arrangements, components, or technologies. Before an innovative design can be realized, or before an
existing design can be evaluated, there must be a common understanding that certain functionalities are
key to successful operation, independent of how these functionalities are accomplished. This report
outlines the framework for navigating through this process for generation, passage, and foundation
modules and defines the objectives, requirements, constraints, and performance that define exemplary
module designs. To frame this line of thinking, the SMH facility concept is shown in Figure 1 with
modules depicted as “black boxes,” that is, without defined shape, form, or configuration.
Figure 1. Conceptual schematic of an SMH facility and constituent modules as “black boxes.” Generation,
passage, and foundation modules will be explored in this report.
3
2. EXEMPLARY DESIGN PRINCIPLES AND CONCEPTS
Hydropower development at a site where no structures have existed before is a complex undertaking with
uncertain outcomes. In the balance are the essential and highly-valued functions of the stream, the
benefits of the renewable energy to be produced, and the costs of creating and deploying technology that
can sustain these stream functions and produce energy concomitantly. Development that does not sustain
stream functions is neither acceptable nor possible in modern regulatory contexts. However, creating and
deploying technology capable of sustaining stream functions while producing power engenders costs that
must be balanced by the revenue and other benefits of power production. This is the essential and
existential challenge for new hydropower technology. The focus of this section is on the hierarchy,
principles, and implementing concepts of SMH functional design that address this challenge.
Traditional hydropower design hierarchy includes components (for example, gates, valves, and switches)
combining to form units (for example, a single turbine-generator) combining to form hydropower
facilities. Multiple hydropower facilities exist in series and parallel within a river and its tributaries and
may be designed, modeled, and operated with greater value to the power system as a combination of
plants than as individual uncoordinated installations. A natural stream environment can also be viewed as
exhibiting a distinct hierarchy—sediment, water, fish, and habitat at a site are constituent elements of a
broader stream network that sustains spatially and temporally diverse ecosystem processes. The stream,
with its flowing water, allocates its power to natural functions: transporting sediment to form the stream
channel; creating habitat for plants and animals; rushing over rocks and boulders to create the rapids,
riffles, and pools that boaters enjoy; providing a riverscape with pleasing aesthetics; and providing
drinking water, to name a few. These natural functions are supported by the lateral inflow of water and
nutrients from a multitude of catchment areas nested within a watershed. Adjacent watersheds and
streams are nested within broader multi-level hierarchical watershed systems.
The broad organizing principle of SMH conceptual design is the acknowledgement of hierarchical order
in streams and hydropower plants and the alignment of stream and module functionality, as depicted in
Figure 2. A module is an independently deployable and operable unit with explicit objectives,
functionality, inputs, and outputs governed by the stream. For example, a generation module transforms
incoming water flow into an energy output and outgoing water flow. A downstream passage module
transfers water, fish, sediment, or boats safely through a facility. An upstream passage module enables
fish to transit upstream safely. A foundation module provides a stable platform that enables itself and
other modules to maintain location and orientation.
A multiplicity of these modules function in complementary and coupled ways within a facility to produce
energy and minimize disruptions to natural stream functions. An SMH facility may include multiple
modules of one type, or different types of modules, to achieve the requisite multi-functionality and scale
for the facility. Facilities in the SMH context exist because electric power from a stream may be possible
and useful, either because of the market value of the energy and power system services made available, or
because the desirable non-power functionality of a facility may be supported or enhanced by the
availability of energy and services.
4
Figure 2. Hierarchical structure of natural stream environments and hydropower systems. The organizing principle of SMH exemplary design is the
alignment of module and stream functionality.
5
2.1 EXEMPLARY DESIGN PRINCIPLES
The design of an SMH facility does not begin solely with a determination of the energy generation
potential and economic feasibility. It should incorporate concepts of environmental function, energy and
energy services, economics, and risk to be robust and successful in the long term. The following design
principles emphasize this concept:
Principle 1: The Exemplary Design Envelope Specification prescribes functionality rather than
detail or methodology. The EDES addresses only a portion of the aforementioned hierarchy of
infrastructure and environment, demanding that stream and power functionality be provided at the
modular and facility levels by fixing explicitly the objectives, requirements, constraints, and performance
that modules and facilities must address. It is not explicit as to which components must combine into a
working module, nor is it explicit as to how multiple SMH facilities interact in series or parallel in a river
system. The requisite multi-functionality of a facility may be wholly specified through the functionality of
the modules and module interdependencies—the detailed design of the modules, including the internal
components, need not be specified for the facility as long as they act to meet the objectives, functional
requirements, and design constraints for modules and facilities.
The EDES does influence, indirectly or implicitly, the component-level specifics and river system
outcomes through the module and facility objectives, requirements, and constraints. It is technology-
agnostic in this way, with no a priori bias toward a specific design; nor is it the one and only design of a
specific facility. Put another way, the EDES indicates what facilities and modules should do rather than
what they should be or how they should accomplish their functions. Multiple designers can create
multiple designs that adhere to the specification and thus are within the envelope. The EDES does not
examine intra-modular functions or component interactions, but instead treats the module as a black box
that meets needs by transforming or transferring inputs of many forms (water, energy, fish, sediment,
boats) into outputs. Multiple unique module designs may achieve the identical and requisite functionality
for a site. The innovation of new components and new combinations of components into these unique
designs is the task of the inventor or designer working in response to the EDES and using the simulation
and testing tools that will be developed under the SMH Simulation and Modeling Plan, the Testing
Capability Plan, and the Multi-Year Research Plan.
Principle 2: Functionality demanded by the Exemplary Design Envelope Specification follows from
the functionality existing in natural streams. This includes basic functionality, such as the transport of
mass and energy; more complex functions, such as provision of habitat; and human uses, such as
recreation and water supply. Figure 2 depicts the commonality of function and correspondence of
hierarchy between the stream resource and SMH technology. Research to develop the SMH Site
Classification Scheme will provide insight into characterization and classification of streams by their
basic and more complex functions and attributes (for example, bed slope, sediment transport, species
presence). The EDES demands that SMH modules and facilities preserve and enhance those functions and
attributes of streams even as they produce electric power and power system services and enable other
human uses. In so doing, it references site characteristics such as gross hydraulic head and flow-duration
or other hydrograph characteristics. This principle provides the essential link between the SMH EDES
research pillar and the SMH Site Classification Scheme pillar. These two research pillars share a common
context of multi-scale hierarchical functionality—from the scale of river basins that transport mass,
energy, and biota, down to the scale of organisms and sediment particles and their interaction with the
internal components of modular technology.
6
Principle 3: The Exemplary Design Envelope Specification parameterizes the functionality of
modules and facilities so as to enable evaluation of cost and feasibility. Feasibility here means
environmental, energy, and economic feasibility and acceptability. This principle requires that the EDES
incorporate sufficient understanding and quantification of functionality, based on available or emerging
science, to enable the designer to design—the EDES must be complete. This principle also requires the
designer to parameterize a specific design so as to couple design choices and attainment of EDES
compliance to costs and feasibility. In other words, designs of SMH modules and facilities must be
explicit and transparent in how they provide stream functionality and in how their costs vary with
functional requirements.
2.2 FEATURES OF SUCCESSFUL FACILITIES
The siting of a hydropower facility in a stream engenders continuous interaction with the environment,
potentially altering the movement of water, energy, fish, sediment, and recreation upstream and
downstream. While there are many potential impacts of hydropower development on stream functionality
that vary with regional and context, the disruption of connectivity is a universal challenge. Practical
mitigation strategies and technologies, and the methodologies to evaluate their success, are the subject of
much research and debate (Bratrich et al. 2004; Poff and Zimmerman 2010; LIHI 2014). Nowhere in the
Exemplary Design Envelope Specification is there a requirement for a dam to completely impound a
stream into a reservoir or pond, nor is there a requirement for an array of modules to span the width of a
stream and entirely disrupt connectivity. This impoundment feature of traditional facility design arises
from two motivations. First, there is value in storing water for flood reduction, water supply, or flexible
power dispatch during peak energy demand periods. It is unlikely that the SMH paradigm can
accommodate these storage-related objectives because they necessarily alter the timing of streamflow—
SMH facilities are run-of-river facilities that do not store water or appreciably alter the inflow
hydrograph. The second motivation for impoundment features is to maximize hydraulic head, thereby
maximizing turbine capacity, enabling streamlined intake design, maximizing hydraulic efficiency, and
maximizing energy production from the available water. The SMH design paradigm addresses this
motivation through tradeoffs between sufficient energy production and functional, but perhaps not
maximum, connectivity of the affected stream.
Success of the Exemplary Design Envelope Specification will be the stimulation of innovative designs
that achieve concomitant functionality of streams and power generation at costs that are feasible. These
designs would use the aforementioned design principles to yield physical arrangements of modules acting
in complementary and functionally-compliant ways to generate head and partition flows to the generation
and passage modules. Ideally, metrics for the functionality of installed modules and facilities would be
available from the outset of SMH design efforts, and many are found in literature and in regulatory
proceedings (Santucci et al. 2005; Schramm et al. 2016; ), reviews (Smith and Jager 2008; Renofalt et al.
2010; Poff and Zimmerman 2010), surveys of plant owners (Trussart et al. 2002), analyses of existing
plant designs (ESHA 2004, Schwartz and Shahidehpour 2006), and best practices frameworks (LIHI
2014; Bishop et al. 2015). Within this body of information, an initial list of features exhibited by facilities
that have achieved broad acceptance and feasibility includes:
predictable and somewhat regular production of electricity;
minimal alteration of the inflow hydrograph (and minimal impoundment);
environmental mitigation technology (functionality) inherent within and integral to the facility design
(including fish passage, water quality, and sediment management design);
minimal disruption to the aesthetics of the natural stream and streamscape;
minimal fluctuations of water surface elevation; and
enabling of safe recreational passage through and activity around the project.
7
However, there is, at best, incomplete consensus on which metrics and which thresholds are appropriate
for development across a range of sites and how to address differing priorities for functionality and
features in facility designs. This is an area where more research and development (R&D) of consensus
among stakeholders will be necessary.
2.3 IMPLEMENTATION THROUGH FUNCTIONAL DECOMPOSITION
The Exemplary Design Envelope Specification decomposes site and stream functionality into facility
level functions, module level functions, and module interdependencies. This functional decomposition
ensures that the stream and site functionality identified through the SMH Site Classification Scheme is
provided by a combination of modules. All facilities must have one or more foundation modules to
prevent physical modules from sliding and overturning. All facilities must have at least one generation
module to produce electric power. All facilities must have at least one passage module to accommodate
flood flows and minimum flows, but most will require additional passage modules to handle
combinations of water, fish, sediment, boats, and debris. These are the primary SMH modules described
in detail in the appendices. The presence of multiple primary modules in a facility requires that the
designer understand and accommodate module interdependencies between water levels, flow, passage
capacity, and power generation. Facilities will also require an interconnection module, a monitoring and
controls module, and an installation/retrieval module. These secondary SMH modules will be addressed in
future appendices to this Exemplary Design Envelope Specification document.
The three design principles of Section 2.1 and the features of successful projects in Section 2.2 are made
explicit within functional decomposition through four design concepts:
Objectives: the primary function to be achieved as a result of deploying and operating a module or
facility. Examples of design objectives are fish passage and power production.
Requirements: a feature of a module or facility that (1) is essential to achieving the primary objective,
(2) is verifiable through testing, measurement, or observation, and (3) in combination with other
requirements indicates that the module or facility is achieving its primary objective. Examples of
requirements are convert hydraulic power into mechanical power with a hydraulic turbine runner
(generation module), or minimize sediment deposition downstream of the SMH facility (sediment
passage module). Requirements are prescribed as functional, performance, interface, or a combination
thereof. Functional requirements relate to the actions a module must perform, performance
requirements are quantified by how well a module must perform a function, and interface
requirements involve interactions with other modules. When prescribed in this way, requirements can
be assessed on both an individual module scale and a holistic facility scale.
Measures of Performance: a set of quantifiable indices or metrics that enable the evaluation of a
module with respect to how well it accomplishes specific and primary technical objectives. Measures
of performance include proportion of fish passing through a module (upstream or downstream fish
passage module), unit efficiency (generation module), or an index of incision potential (sediment
passage).
Constraints: a limitation on the value of a design parameter or a limitation on an effect of deployment
or operation that must be satisfied and verifiable to ensure feasibility of a module or facility.
Constraints include avoid creating a recirculating hydraulic jump under normal conditions (recreation
passage module), and must be run-of-river and operate within natural variations of head and flow
(generation module).
These concepts define the design challenge for facility and module technology developers. Each of
Appendices A through G specify the design concepts for a module type, along with supporting rationale
8
for those concepts. Technology developers will undertake research efforts to iteratively design, simulate,
fabricate, and test the performance of their equipment until it satisfies the design concepts, including
design constraints for installed cost. The input/output specifications for a specific module design will be
required to evaluate module interdependencies and establish the exact arrangement of modules in a
facility design.
9
APPENDICES
A. GENERATION MODULE
B. FISH PASSAGE MODULE
C. SEDIMENT PASSAGE MODULE
D. RECREATION PASSAGE MODULE
E. WATER PASSAGE MODULE
A-1
APPENDIX A. GENERATION MODULE
The generation module is envisioned as a complete hydroelectric generation machine, meaning the
module contains all equipment and systems for safe and reliable water power generation, it is pre-
engineered to accommodate a host of potential sites, the internal component configuration is predictable
and scalable, performance characteristics meet preconceived expectations, and the module can be relied
upon to produce a regular supply of hydropower. The generation module is the only module designed to
produce electricity and is a module that will be deployed at all SMH facilities.
A.1 OBJECTIVES
The primary objective of the generation module is to generate hydroelectric power from flowing water
under pressure.
The following specific objectives need to be accomplished to achieve the primary objective:
1. Take in flow a. Receive a flow of water driven by a pressure gradient.
2. Direct the flow to the hydraulic turbine chamber a. Pass flow through to the hydraulic water turbine.
b. Adjust the direction of the flow for optimal power extraction. The adjustment typically
takes place with stay vanes and/or fixed or adjustable inlet guide vanes.
3. Convert hydraulic power to mechanical power a. Water flow does work on the runner as the force of moving water acts across the runner
blades.
b. The runner blades rotate about a fixed axis, generating torque (either on a shaft or
through torque-transmitting connections between turbine runner blades and the generator
rotor) with a magnitude that is a function of the hydraulic forces and distances they occur
from the axis of rotation. Runner blades can have a fixed or adjustable pitch.
4. Convert mechanical power into electrical power a. The mechanical work derived from the runner is used to spin the generator’s rotor, which
carries a static magnetic field produced by either permanent magnets or windings
(electromagnets).
b. The rotational motion creates a time-varying magnetic field in stationary conductors
surrounding the rotor. The time-varying fields induce electric fields, which ultimately
cause electric current to flow. In many cases, power electronics converters are used to
control the generator with respect to various flow conditions, power demand, and optimal
operation.
5. Prepare electrical power for distribution to the customer a. The power produced by the generator is made compatible with the specifications and
power quality requirements of the customer. In many cases, this involves power
electronics converters that synchronize with the grid and provide sufficient filtering for
power quality requirements.
6. Release flow a. The residual flow kinetic and pressure energy carries water out of the hydraulic turbine
chamber and out of the module. For some arrangements, a draft tube helps recover kinetic
Generation Module Primary Objective
To generate hydroelectric power from flowing water under pressure
A-2
energy by diffusing the flow and slowing the water flow velocity into the tailwater,
effectively increasing head across the turbine.
7. Integrate structurally into the foundation module
a. The entire generation module must integrate structurally and functionally into the
foundation module to transmit forces directly into the ground and ensure module
stability.
The specific module objectives are shown in Figure 3, and Figure 4 maps these objectives onto a
schematic of a conventional hydropower facility. The upstream and downstream module boundaries will
intake and release flow, respectively, and the conversion of hydraulic power to mechanical power and
finally into electrical power will occur inside the module. The requirement to prepare electric current for
distribution is ambiguously placed at the module boundary. An interconnection module will be used to
distribute electrical power to the customer, whose requirements will dictate the inner workings and
functionality of the interconnection module. It is possible that a generation module will consist simply of
conductors at the generator terminals that send raw electrical power to the interconnection module.
Another possibility is the inclusion of power electronics and other auxiliary electrical equipment within
the generation module itself.
Figure 3. Conceptual schematic of the specific objectives of a generation module.
A-3
Figure 4. Specific objectives from Figure 3 mapped on a conventional run-of-river hydropower facility.
A.2 REQUIREMENTS
Generation module requirements state the conditions that must be met to accomplish the generation
module primary objective. Stated simply, requirements describe what the module has to do. They include
specific objectives, as well as additional sub-requirements that enable the specific objectives. In the
conventional sense, hydroelectric generation is achieved through the mechanical coupling of a turbine
runner to a generator; the turbine runner is placed in a hydraulic chamber within a water conveyance, and
the generator is placed in a powerhouse. Hundreds to thousands of additional interacting components are
incorporated into the design, each with a dedicated functionality and well-defined requirements. These
components are engineered and optimized to achieve maximum hydraulic, mechanical, and electrical
efficiency. The goal of generation module conceptual design is to remain uncommitted to these specific
components, arrangements, technologies, and design decisions in the early stages of design thinking and
consider the module as technology-agnostic. Regardless of design or generation technology, generation
modules must exhibit certain functionalities to ensure successful operation. Multiple module designs may
achieve the same functionality through physically and structurally unique technologies and
configurations. The intent of this section is to identify these functionalities through the specification of
requirements, rather than structure, components, configuration, and technology.
The generation module functional requirements are stated succinctly in Table 1 and described with a
formal definition.
A-4
Table 1. Generation module requirements. In the fourth column: F = Functional; P = Performance; I =
Interaction; O = other. In columns 6–11, an “X” denotes a relationship to the river continuum constituent indicated
in the top row
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter q
ua
lity
1 Intake flow
a Guide upstream flow to the
generation module intake F, P, I
The intake is the primary point
of entry for power production.
Improper intake design runs
the risk of reducing installed
capacity by introducing
unnecessary head losses and
increasing down time and
operations and maintenance
effort by allowing trash and
debris to accumulate at the
entrance. Key intake design
considerations include location
and orientation, type of intake,
hydraulic convergence and
head losses, and depth of
submergence
X X
b Provisions for shutoff F, P
A generation module should
incorporate a mechanism to
stop flow through the runner.
This may include a gate at the
module intake or the use of
adjustable blades
X X
c Provisions for trash racks F, P
Any trash or debris allowed
through the intake into the
hydraulic chamber has the
potential to damage equipment,
disrupt operations, and require
downtime and maintenance
expense. Debris larger than the
spacing between runner blades
may remain lodged in the
module unless the blades rotate
with sufficient force to
dislodge it or chop it into
smaller segments. A trash rack
will mitigate this issue, though
it will introduce additional
head losses and design
considerations with respect to
placement, bar spacing,
cleaning ability, weight, and
extent of mechanical
complexity
X X
A-5
Table 1. Generation module requirements (continued)
Requirement Type
(F/P/I/O) Formalization/rationale
En
ergy
Water
Fish
Sed
imen
t
Recreatio
n
Water q
uality
2 Direct flow to the hydraulic
turbine chamber
Adjust the direction of the
flow for optimal power
extraction
F, P
Reaction turbines are
optimized based on the concept
of velocity triangles —the flow
must enter the turbine chamber
at the correct angle and
velocity to maximize power
extraction. The adjustment
typically takes place with fixed
or adjustable inlet guide vanes
X X
3
Convert hydraulic power into
mechanical power with a
hydraulic turbine runner
Maximize the work done by
the fluid on the runner blades F, P
The water flow does work on
the runner as the force of
moving water acts across the
runner blades. The runner
blades rotate about a fixed
axis, generating torque (either
on a shaft or through torque-
transmitting connections
between turbine runner blades
and the generator rotor) with a
magnitude that is a function of
the hydraulic forces and
distances they occur from the
axis of rotation. Runner blades
can have a fixed or adjustable
pitch
X X
Optimize turbine shape, size,
number of blades, and speed
to minimize head losses
across the runner associated
with turbulence, disk friction,
and leakage
F, P
Specific turbine runner
characteristics must be
optimized to maximize power
conversion and minimize head
losses associated with
turbulence and mechanical
friction. Simulation and
physical testing of prototype
designs is a critical component
of turbine design optimization.
X X
4 Convert mechanical power
into electrical power
a
Encompass all equipment
and systems for safe and
reliable electricity generation
F
The generation module is
envisioned as an integrated
water-to-wire module that
contains a hydraulic water
turbine, generator, controls,
X X
A-6
Table 1. Generation module requirements (continued)
Requirement Type
(F/P/I/O) Formalization/rationale
En
ergy
Water
Fish
Sed
imen
t
Recreatio
n
Water q
uality
and electrical equipment
within a single unit. All
equipment and systems,
including governing units and
systems, speed controllers, and
power electronics, should be
incorporated into the
generation module
b
Optimize generator speed
control for ease of use, low
cost, and compactness
F, P
The rotational speed of the
generator must remain constant
if it is directly connected to a
power supply, or it must be set
by power electronics. An
optimal configuration will
minimize the need for
peripheral equipment
X X
5 Prepare electrical power for
distribution to the customer
a Send electrical current to
interconnection module F, P
Electrical characteristics, e.g.,
voltage, short circuit ratio,
reactance, line charging
capacity, etc., must
conform to the interconnected
transmission system
X
6 Release flow
a Maximize kinetic energy
recovery out of the module F, P, I
For some arrangements, a draft
tube helps recover kinetic
energy by diffusing the flow
and slowing the water flow
velocity into the tailwater,
effectively increasing head
across the turbine. The type,
size, and arrangement of the
draft tube must be optimized
based on the turbine design,
tailwater setting, and cavitation
characteristics
X X
7 Integrate structurally into
foundation module
a
Transmit all forces through
non-critical components into
the foundation module
F, P, I
The generation module will be
supported instream by a
foundation module that serves
as an interface to the
streambed (rather than a
conventional powerhouse).
X
A-7
A.3 INPUTS, FUNCTIONAL RELATIONSHIPS, AND PROCESSES
In this section, we identify the key processes and relationships related to the conversion of inflow
hydraulic power to electrical power. Many basic relationships are available in textbooks and manuals on
hydropower design (for example, see Gulliver and Arndt 1991; ASME PTC 1993; Leyland 2014).
Because the hydropower turbine is the primary revenue-generating mechanism in any hydro project,
functional relationships that govern specific runner and generator types, shapes, and operating
characteristics are often proprietary, developed and optimized based on years of detailed laboratory and
computational studies. To strike a balance between common knowledge and proprietary information, this
section broadly discusses the most important processes for generation module design.
A.3.1 Necessary Inputs
The key processes identified in the previous section rely on necessary site inputs and variables that must
be known by a technology designer and developer. A summary of these inputs is outlined in Table 2.
Table 2. Necessary inputs for generation module design
Identification of
key inputs Formalization
River discharge Flow duration curve, mean annual flow, minimum environmental flow
requirements
Head Range of gross head available (headwater and tailwater high and low
elevations), net head, tailwater submergence
River geometry Wetted perimeter, width, bottom width
Electrical frequency of customer AC frequency of the customer to which generation module must be
synchronized
Desired power quality Total harmonic distortion, power factor
Voltage The output voltage desired at the grid or customer connection prior to
high voltage transformers for transmission.
A.3.2 Functional Relationships
The functional relationships that govern generation module operation, along with a brief summary of their
importance, are described in Table 3.
Table 3. Functional relationships governing the generation module operation
Relationship of To Rationale/Importance
Site characteristics Range of head and
flow
The conventional approach to small, low-head hydropower relies
on an impoundment model, which assumes a dam is placed across
a stream to create sufficient head or a pool for power generation.
New functional relationships are necessary to determine how
head and flow may vary at a site with a modular facility that does
not use an impoundment.
A-8
Table 3. Functional relationships governing the generation module operation (continued)
Relationship of To Rationale/Importance
Range of head and
flow
1. Performance
characteristics
2. Rotational speed
3. Turbine runner
diameter
4. Cost
1. Relationships between design head and flow and important
turbine performance characteristics are necessary to establish how
a generation module will operate at a given site. These include
power output vs. head and flow, torque vs. head and flow, and
hydraulic efficiency vs. head and flow.
2. The rotational speed of the turbine can be derived from the
specific speed, once the head, flow, and power potential of a site
are known.
3. The turbine runner diameter is specific to the manufacturer and
runner design, and it may be developed empirically based on
physical testing. Relationships defining how generation module
runner diameter varies with head and flow are necessary to
standardize module development.
4. Standardized and scalable cost estimates will be necessary to
determine if a module design is economically feasible.
Module scaling
Hydrologic statistics
and module
performance
characteristics
The traditional approach to determining how many hydropower
turbines are necessary at a site is based largely on the flow
duration curve, annual hydrograph or other flow statistics, and
turbine performance characteristics. This will be a starting point
for assessing generation module scalability.
Specific speed Turbine shape
In conventional turbine design, specific speed, a function of head,
flow, and rotational speed, determines the type of turbine that is
most appropriate at a given site. A new relationship for
generation modules may be necessary if turbine runners do not
conform to conventional geometries.
Input hydraulic
power
Shaft power and
output electrical
power
Turbine efficiency describes how well a module turbine converts
input hydraulic power to shaft power, while unit characteristics
describe the efficiency in converting input hydraulic power to
electrical power. Both of these efficiency estimates of generation
modules must be known for a wide range of head and flow to
inform techno-economic models of site feasibility.
The generation module primary objective can be partitioned into three main concepts: generate power,
flowing water, and pressure. The first is a function of the latter two, that is, the power output of the
module, P, is a function of the water flowing through the module, Q, and the pressure available to the
module from the flowing water, generally referred to as hydraulic head, H. Power is also a function of the
energy losses sustained during conversion of hydraulic power to mechanical power and the conversion of
mechanical power to electrical power:
𝑃(𝑡) =𝑄𝐻𝜂𝑡𝜂𝑔
11,814 (A.1)
where P(t) is electrical power output of a generation module in MW, Q is flow discharge through the
turbine in cfs, H is hydraulic head in ft, 𝜂𝑡 is the hydraulic turbine efficiency, 𝜂𝑔 is the generator
efficiency, and 11,814 is a conversion constant for English units. The four variables on the right hand side
of the equation are all a function of the surrounding environment, module component structure and
architecture, and numerous other uncontrollable and external inputs that vary as a function of time. To
provide a more standardized approach to generation module functional analysis, the important
relationships describing the flow of water to the module, the conversion of power in the module, and the
flow of water out of the module will be presented.
A-9
A.3.2.1 Flow of water to the module
A holistic approach to generation module design must begin with an assessment of the local hydrologic
regime, namely the duration, magnitude, and frequency of river discharge and the flow available for
power generation. Flow availability is most commonly expressed using a flow duration curve, a function
that represents the percentage of time a certain volumetric flow rate has been observed at a specific point
in space over a previous time period. The flow duration curve can be plotted with the estimated gross
head available to provide a clear picture of the variability in power generation potential at a given site
(Figure 5). The flow duration curve provides a range of discharges that are important to generation
module design:
The minimum observed flow provides a baseline to what has historically been observed in the stream.
The design flow represents the point where a generation module or modules are optimized for cost and
energy production.
The minimum technical flow reflects the point where a generation module cannot technically operate
because of low efficiency and potentially equipment damage from off-design operation. The minimum
technical flow will vary by number of generation modules and the efficiency characteristics of each
module.
It is assumed the generation module will not have access to the full river discharge, as the module(s) will
occupy a total width that is less than the total width of the stream. When the use of passage modules is
necessary, the river discharge must be partitioned among passage and generation modules in a way that
accommodates the objective of each module. The greater the flow needs of the passage modules, the
closer the minimum technical flow line moves toward the design flow line, and the smaller the design
range becomes. The optimum design flow will be less than the largest magnitude of observed flow—if the
generation module(s) are sized based on a discharge that occurs only 1% of the time, they will be idle or
operating under potentially damaging off-design conditions for extended periods of time, and there is
little economic payoff in sizing a turbine for 1% of the time.
As shown in Figure 5, the flow of water available to the module will be closely related to the gross head
at a given location, with a relationship determined by the geometry of the stream and the characteristics of
upstream or downstream hydraulic structures, among other factors. The flow and head interdependencies
are particularly important for the design of low-head generation modules. At most low-head run-of-river
sites, the tailwater elevation generally rises twice as fast as headwater elevation when river flow
increases, leading to a significant reduction in available gross head (Kinloch 2015). As a result, low-head
sites with high variability in flow and head often lead to operating conditions beyond the acceptable
performance and efficiency limits of the hydraulic turbine.
A-10
Figure 5. Example flow duration curve with important flow design parameters.
Variability at low head presents a significant design challenge for both conventional turbines and
generation modules. The following are some of the major obstacles to success.
Turbine runner diameters must be larger to accept larger volumetric flow rates and produce an
equivalent power as head is decreased. Larger diameters require more material to resist the internal
forces and stresses of operation, increasing the weight of the machine and the structural support (i.e.,
civil works) requirements. The result is a lower power output per unit weight of material and per site
cost, which is economically unappealing.
Generating units must maintain high efficiency over a wide range of possible head and flow
combinations to achieve economic feasibility and to avoid operating in off-design conditions that may
increase the likelihood of premature machine failure or damage. From a hydraulic perspective, this can
be accomplished by adding adjustable guide vanes and adjustable turbine blades that rotate based on
flow and head to provide the optimum velocity angles for the hydraulic turbine runner. This
arrangement requires additional mechanical complexity and cost, and the flow and head characteristics
of a given site must be analyzed to determine if the additional efficiency gains justify the added cost.
From an electrical perspective, higher overall efficiencies can be achieved through the use of power
electronics that allow the turbine to operate at variable speeds, although additional costs and electrical
complexity may also be incurred.
A standardized approach to characterizing water flow to modules has been embodied in the hydrologic
classification work of McManamay et al. (2013), who classified 12 hydrologic regimes throughout the US
based on flow statistics (Table 4).
A-11
Table 4. US hydrologic classification (McManamay et al. 2013)
Name Code Characteristics
Intermittent flashy IF High intermittency, long high-flow duration
Perennial runoff 1 PR1 Similar to SHBF but lower base flows, semi-stable
Perennial runoff 2 PR2 Similar to PR1, but lower base flows, higher runoff than PR1
Unpredictable intermittent 1 UI1 Moderate intermittency, low predictability, and semi-flashy
flows
Stable high base flow SHBF High base flows (smaller than SSGW), stable and relatively high
runoff
Snowmelt 1 SNM1 Distinct and consolidated periods of runoff, stable and relatively
high base flows, early annual minimum (winter freeze)
Super-stable groundwater SSGW Very high base flow, high stability, not necessarily high runoff
Coastal high runoff CHR High runoff, very late annual maximum, and very early annual
minimum; slightly high reversals (potential tide effects)
Unpredictable intermittent 2 UI2 Moderate intermittency, low predictability, and semi-flashy
flows (different timing and runoff from UI1)
Snowmelt 2 SNM2 Less stable and lower base flow than SNM; otherwise similar
Western Coastal high runoff WCHR Distinct wet/dry seasons, lower base flow than PR streams, but
very high runoff, early annual maximum
Harsh intermittent HI Very long periods of intermittency, punctuated by episodic
flows
A.3.2.2 Converting hydraulic power to mechanical power
Inflow hydraulic power is converted to mechanical power through runner blades, which rotate about a
fixed axis generating torque, either on a shaft or through torque-transmitting connections between turbine
runner blades and the generator rotor. It is anticipated that the generation modules (based on both new and
traditional designs) will be fully immersed in water, which necessitates the use of a reaction-type turbine
design in which the runner blades are profiled to create a lift force that generates torque. Therefore, the
inflow hydraulic power available to the generation module is
𝑃ℎ =𝑄𝐻
11,814 , (A.2)
which is the same as Eq. (A.1) without the efficiency terms. In this case, Ph is hydraulic power in MW
and represents the maximum theoretical power available from the stream. The mechanical power
delivered to the generator by the turbine is
𝑃𝑡 = 𝑃ℎ𝜂𝑡 = 𝜔𝑇 , (A.3)
where Pt is turbine power, ηt is turbine efficiency, ω is the rotational speed of the turbine shaft in rad/s,
and T is the torque provided by the turbine shaft.
To optimize turbine power, i.e., the generation of torque, the turbine runner diameter and rotational speed
must be suited to the design head and flow. The relationship between these two variables at a given head
is
𝑁𝑡 ∝1
𝐷𝑡 , (A.4)
A-12
where Nt is the rotational speed of the runner in rpm and Dt is the turbine diameter. This inverse
relationship indicates an increase in rotational speed is correlated with smaller-diameter turbines, and
larger turbines have a slower rotational speed. This tradeoff has several implications for module design:
A reduction in runner diameter will decrease material costs, increase runner rotational speed, and
decrease generator size and cost. However, disadvantages are manifest in increased fluid velocities—
which require specific cavitation avoidance techniques, including a lower unit elevation setting and
concomitant increased excavation burden—and high runaway speeds, which exert substantial
mechanical forces that must be sustained safely by the turbine. Smaller-diameter turbines also pass
less flow, generate less torque, and produce less power per unit than larger-diameter turbines.
A larger turbine size will increase material costs and may require the use of a speed increaser or gear
box to drive the generator at a faster speed than that of the runner. The gear box will result in
additional efficiency losses, noise, vibration, and cost; but the overall cost may be offset by the use of
a standard or off-the-shelf generator that would otherwise be unsuitable without the gear box. Higher
civil works costs may result from the larger runner.
To obtain the efficiency characteristics of a generation module, that is, to know how well the module
converts hydraulic power to mechanical power, it is necessary to conduct model or prototype testing
under a range of different operating conditions. Statistical formulae describing optimal module
dimensions and performance characteristics must be developed based on iterative testing procedures that
measure turbine efficiency over a range of head and flow. High efficiency is required to ensure favorable
hydrodynamic behavior, which must be maintained to maximize both the turbine life and annual energy
production, and minimize the negative impacts of cavitation and vibration. In general, water turbines have
some optimum range of head and flow within which they should operate, and some boundary of head and
flow within which they must operate to avoid off-design conditions that may damage equipment and
systems. An example of these turbine characteristics is shown as a hill chart in Figure 6. For this
particular turbine, the optimum efficiency can be obtained over a range of heads within a relatively
narrow band of expected unit discharges. The goal of exemplary design is not to maximize the peak
efficiency but to obtain a broad and tall optimum efficiency band that indicates good performance under a
range of conditions.
Figure 6. A hill chart documenting the hydraulic efficiency (shown as labeled contours) of a water turbine at
various head and flow combinations. The dashed lines represent a forbidden zone within which it is inefficient and
potentially damaging to operate the turbine. (Cordova et al. 2013)
A-13
There are two concepts associated with turbines and speed: rotational speed and specific speed.
“Rotational speed” refers to the number of revolutions per minute the runner will make under given
inflow conditions. The rotational speed of the runner is proportional to head and flow and must be
synchronized, either directly by mechanical means or indirectly through power electronics, to the
frequency of the grid, which is 60 Hz in the United States. “Specific speed” refers to the nondimensional
number used to classify turbines based on their performance and proportions. There are numerous
mathematical representations of specific speed, each of which incorporates some combination of head,
flow, rotational speed, diameter, and power output. Engineering experience has proved that different
shapes and orientations of runner blades will result in optimum performance at particular specific speeds
(Figure 7). A generation module employed at low head will have a relatively high specific speed,
correlating with a conventional axial flow type machine.
Figure 7. Optimum runner blade geometry for a given specific speed. (Baines 2010)
A.3.2.3 Converting mechanical power to electrical power
Just as flow across turbine blades produces a torque that spins the turbine, electric current through the
generator stator windings produces a torque on the generator’s rotor. To convert the mechanical power
captured by the turbine into electric power, the electromagnetic torque opposes the hydraulic torque. That
is, hydraulic currents will tend to increase the rotor speed, whereas electrical currents will tend to
decrease the rotor speed. A quasi-steady state is reached when these two forces come into equilibrium.
Therefore, special attention must be given to the generator design for variable head and flow, as is the
case for the turbine design. Moreover, the turbine and generator design must be matched to a certain
degree, as it is the intersection of their feasible torque/speed operational ranges that produces the unit
level power and efficiency characteristics. The generator real power output is given as
𝑃𝑔 = 𝑃ℎ𝜂𝑡𝜂𝑔 , (A.5)
where ηg is the generator efficiency and Pg is generator power in kilowatt. Generator apparent power in
kVA is expressed as Pg/pf, where pf is the power factor, a value that conveys how efficiently the generator
transfers energy to a load.
The generator must rotate at a certain speed to produce electrical power with a voltage and frequency that
match the power system of the customer. The required speed range of the generator will depend to a great
extent on choices made upstream in the generation module. Adjustment of the flow at the inlet of the
module, or adjustable turbine vanes that attempt to mechanically govern the speed of the
turbine/generator, will reduce the speed range required by the generator, allowing it to be more highly
A-14
optimized for a specific operating condition. On the other hand, a generator system with an inherently
wide speed range may obviate the need for mechanical governing mechanisms, resulting in lower-cost
turbines. If both mechanical and electrical speed regulating mechanisms are present, the design and
control of the turbine and generator become tightly coupled. This gives the potential for high-performance
designs at the risk of increasing the cost of the overall system. The goal of the designer will be to assess
the tradeoffs between performance and cost in optimizing the module behavior.
Generators require a minimum speed to produce their rated power, sometimes called the “base speed.”
The power output will generally drop linearly below this speed. For a given generator topology, the
generator size is determined by the ratio of maximum power to base speed. Higher base speeds and lower
power ratings lead to smaller generators.
There are three main considerations in designing a generator for wide speed range operation. First, the
generator voltage should be controlled within the designed limits over the entire speed range. Second, the
generator—and any associated power electronics—must supply power to the grid at a fixed frequency.
Third, because they are made of steel and windings, generators are inherently inductive in nature and tend
to have a lagging power factor if special attention is not paid to this fact. For a generator to produce its
rated power over a wide speed range, it is desirable for the power factor to be as close to unity as possible.
The addition of a magnetic field produced on and carried by the rotor moves the power factor from
lagging toward unity. The method of producing and controlling the rotor field is the main difference
between different generator topologies and their power electronics requirements. These topologies include
wound field synchronous generators, permanent magnet synchronous generators, and various types of
induction generators (Skvarenina and DeWitt 2004; Hughes 2009). Figure 8 shows the power-speed
characteristics of an idealized generator achieving a constant power speed range of 5:1.
Figure 8. Idealized generator system power-speed characteristics for wide speed range operation. Units are
displayed in pu (per unit), a fraction of an arbitrary base unit quantity.
For generators with wound field rotors with DC excitation and slip rings, the rotor field is proportional to
the applied voltage; and the field can be reduced to allow higher-speed operation within the voltage
limitations of the generator. In this case, however, the generator frequency is proportional to the rotor
speed, and some form of AC-AC conversion is necessary to supply power at the grid frequency. It is
A-15
possible to adjust the rotor field to regulate and operate at a fixed speed, thereby permitting direct
connection to the grid without power electronics. However, doing so will often result in lower power
density and efficiency than other arrangements.
Synchronous generators are so named because they produce electrical power at a frequency directly
proportional to the rotor speed. Types of generators in this category include surface-mounted permanent
magnet, synchronous reluctance, and interior permanent magnet generators (PMGs). AC-to-AC
conversion is necessary for supplying power to the grid if they are not operated at a fixed speed. Wide-
speed-range operation is accomplished in PMGs by creating a field in the stator that actively cancels a
portion of the field setup by the rotor. This has a similar effect to reducing the rotor excitation in a DC
generator. Because of bulky windings and conduction losses in the rotors of wound field and induction
generators, PMGs are often more efficient with smaller, lighter rotors.
Rotor field generation occurs naturally in singly-fed induction generators because of a difference between
the mechanical speed of the rotor and the rotational speed of the electric field produced by the stator.
When directly connected to the grid, induction generators can supply power synchronously to the grid
with a variable rotor speed, although the peak efficiency/power region can be quite small. With the
inclusion of power electronics and a suitable control algorithm, their performance can be quite robust over
a wide speed range.
Doubly-fed induction generators accomplish wide-speed-range operation by supplying variable AC
frequency excitation to the rotor. The frequency is controlled so that the power produced by the generator
is at the grid frequency. Therefore, the generator is able to supply power directly to the grid without
power electronics, while the power electronics exciting the rotor need only be rated at a fraction of the
output power.
The inclusion of power electronics to perform a frequency conversion between the generator and the grid
allows a decoupling of the generator operation from the grid frequency. This can result in significant
volume, weight, and cost reductions if the generator can be designed to operate at a higher speed than
would otherwise be dictated by the grid frequency. Of course, this advantage is offset by the cost and
complexity of the power electronics system, which must be rated at full power. Since the inverter is
connected to the rotor of a doubly fed induction generator, it must still operate (nominally) at
synchronous speed; and no generator sizing benefit results from the inclusion of the power electronics.
However, the inverter for a doubly fed induction generator is sized relative to the required speed range
and can be rated at a much lower level than the maximum generator power.
A.3.2.4 Flow of water out of the module
The generation module must recover as much energy as possible from the flow as it is discharged from
the hydraulic turbine chamber, while maintaining sufficient pressure head to overcome the pressures
exerted by the tailwater. This is generally accomplished using a draft tube, which works to diffuse or slow
the linear and rotational velocity of the water, increasing the pressure head and the overall head across the
turbine. This is especially important for reaction-type turbines at very low heads, during which the
velocity head of water leaving the runner may increase to 80% of the net head available to the runner
(ESHA 2004).
The draft tube allows a turbine runner to be placed above the tailwater elevation, allowing ease of access
for maintenance and reduced excavation burden during construction. These features are preferred in
module design. At a certain elevation, cavitation may occur when the local absolute pressure in the
turbine or draft tube drops below the vapor pressure of water. Thus, the tailwater setting must be
optimized for efficiency, cavitation prevention, and cost. According to Bishop et al. (2015), the current
A-16
practice in hydropower design is to lower the turbine centerline and use a long, wide draft tube to
optimize efficiency, although trading off efficiency for more economical configurations with lower civil
costs is a viable strategy.
A.4 MEASURES OF PERFORMANCE
The primary generation module performance measure is the ability to generate revenue to support
development of the SMH project. From an equipment perspective, this measure requires simultaneous
knowledge of the module unit efficiency characteristics, scalability, size of the module, and installed cost
per module, in addition to estimates of module useful life and maintainability. A single value cannot be
specified for any of these categories, but general targets are offered that should be achieved by generation
modules.
A.4.1 Module Unit Efficiency Characteristics
Standard of measurement Target
How well the module converts hydraulic
input power to electrical power
High unit efficiency over a wide range of heads and flows. A lower
peak efficiency may be acceptable if overall generation module costs
are reduced for the same estimated useful life, but the efficiency
must still remain high at partial load
Hydraulic water turbine and generator peak efficiencies are generally greater than 85–90% with modern
small hydropower technologies. The range of turbine efficiencies at different flow rates for a given head
is highly dependent on the module configuration. Reaction-type axial flow turbines with adjustable blades
and gates can achieve high efficiencies from partial load to greater than full load, while propeller type
turbines with fixed blades and gates have a sharp peak efficiency that quickly falls off at loads below and
beyond the design load (Figure 9). For the low-head and run-of-river types of applications targeted by
SMH, some adjustment of gates or blades is necessary to ensure efficient operation at partial load.
Figure 9. Turbine efficiency for different turbine types at constant speed as a
function of percentage of full load. (Farell et al. 1983)
An additional influence on module unit efficiency is the speed of operation. Fixed-speed turbines and
generators must mechanically synchronize to the grid using the head and flow available at the site. If head
A-17
or flow is increased or reduced, the turbine unit must compensate by adjusting the flow rate if possible, or
by stopping generation completely, resulting in a narrow range of operation and efficiency (turbine type C
in Figure 9). Variable-speed operation is enabled by power electronics, which decouple the turbine and
generator from the grid. The turbine is allowed to rotate at an optimal speed, and a series of rectifiers and
inverters act to maintain a constant output frequency and voltage. The result is both an increase in
efficiency over a range of heads, and an expansion of the effective operating range of the unit (Figure 10).
Although it is expected that a generation module should achieve peak efficiencies similar to those of
existing technologies, it is possible that a lower-peak-efficiency turbine with lower overall installed cost,
reduced operating and maintenance costs, and low replacement costs could prove economically viable.
However, the peak efficiency should be maintained under the variable heads and flows that are to be
expected at low-head sites. This operation would require the use of advanced turbine control or double
regulation.
Figure 10. Example of the performance improvement expected from variable-speed
turbines with adjustable gates. (Farell et al. 1983)
A.4.2 Scalability
Standard of measurement Target
How well the module can be applied at a
variety of sites with different flow
regimes
Module consists of a standard turbine runner and generator available
in a range of installed capacities
Most small hydropower turbine manufacturers offer a range of standard turbine runner diameters, while
fewer incorporate the generator directly into the design or offer a combined turbine and generator
package. To provide a standard approach to site analysis, a generation module should incorporate both the
turbine runner and diameter in a variety of standard sizes. This enables scalability to be addressed in two
ways—the generation module can be applied at many different locations, and multiple generation
modules can be applied at a single site. When turbines are designed in this fashion, module service,
replacement, refurbishment, and spare part service and administration can be streamlined and made cost-
effective.
A-18
A.4.3 Size
Standard of measurement Target
Overall dimension of a fully operating
module
Modules or sub-modules are amenable to standard transportation
methods and facilitate ease of installation and minimized civil works
Module size is largely influenced by generator type and arrangement. A smaller turbine may be less
expensive to manufacture, but it will accept lower volumetric flow rates, generate less power, and may
require a speed increaser (gear box or belt drive) to use a standard and compact generator. This additional
equipment will increase the overall module size and nominally reduce module unit efficiency, although it
generally will lead to an overall reduction in project costs. Larger turbines will accept more flow and
produce more power at the same head. A larger turbine may not require a speed increaser, although its
increased size will generally require additional structural support and civil works.
The use of an embedded generator design, in which the generator is configured either in a hub on the nose
of the runner or on the runner blades as a rim-rotor type unit, can reduce the overall footprint of the
turbine and generator configuration, resulting in reduced civil work, simplified electrical configurations,
and reduced installation times. These turbines generally exhibit larger diameters than conventional
designs with an equivalent rated power (Figure 11). However, all three embedded designs in Figure 11
use PMGs with the option of variable-speed technology, reducing the balance of auxiliary equipment
associated with excitation systems and the number of rotating parts while increasing the operating range
of the unit. They are also fully submersible, eliminating the need for a powerhouse and additional civil
works to protect a conventional generator. This produces cost benefits as well as aesthetic value—the
reduction in size of the superstructures improves the integration of the entire facility into the surrounding
environment.
Although no target size is set for a generation module, the following guidelines are offered:
Modules must be amendable to standard transportation methods—a single module or sub-modules
should not be larger than the carrying capacity of a standard semi-trailer.
Designs should enable quick and efficient assembly and disassembly of modules or sub-modules.
Ease of installation should be a priority—thus compact modules or sub-modules that can be lifted into
and out of place within a day are preferred.
Modules that limit the need for civil works are preferred.
A-19
Figure 11. Single runner diameter for small, low-head (<10m) conventional hydropower turbines1 (bulb
Kaplan, vertical Kaplan, Francis) and embedded generator designs (Amjet2, VLH
3, StreamDiver
4).
A.4.4 Installed Cost
Standard of measurement Target
How much it costs to manufacture,
deliver, and install the module
The immediate target for an SMH project should be less than
$6,000/kW, including all modules necessary at a site. Over time, this
number should be reduced as module deployment increases.
There is a large degree of uncertainty in setting a specific target installed cost for a generation module:
A site may consist of a generation module and a foundation module, or it may require several passage
modules and foundation modules. The acceptable installed cost of generation equipment will be
different in each case.
The cost to procure, deliver, and install a generation module may be greater than the cost of existing
technologies, but the modular development of a project may reduce civil works and other project soft
costs, improving project feasibility.
A generation module manufactured and tested offsite, delivered as a complete unit skid-mounted to
the project location, and installed in roughly a day is expected to yield significant cost savings for a
project, but this theory is largely untested in the market.
1 Data obtained from http://www.koessler.com/en/kaplan-turbines and http://www.koessler.com/en/francis-turbines
2 Data obtained from http://amjethydro.com/products.html
3 Data obtained from http://www.vlh-turbine.com/gamma
4 Data obtained from http://voith.com/ca-fr/t_3390_StreamDiver_screen.pdf
0
1
2
3
4
5
1 10 100 1000 10000
Dia
met
er (
m)
Rated Power (kW)
Bulb Kaplan
Vertical Kaplan
Francis
Amjet
VLH
VLH
StreamDiver
A-20
The first modular generating units developed and installed may reflect higher R&D, design, and
engineering costs; but as economies of scale are achieved, cost savings will be realized.
Based on these uncertainties, it is most instructive to set an upper bound on the installed cost under which
a generation module should strive to achieve. This can be estimated by looking at installed capital costs of
new stream-reach development projects in the United States (O’Connor et al. 2015), as these best reflect
what is currently economically feasible. Small, low-head hydropower projects in the planning,
engineering, and construction phases exhibit installed capital costs between $2,000/kW and $11,000/kW,
with planning stage projects reflecting higher costs owing to contingencies and low-accuracy cost data
(Figure 12). The majority of low-head engineering stage projects are in the range of $2,000/kW to
$7,000/kW. The immediate target for an SMH project should be less than $6,000/kW, including all
modules necessary at a site. Over time, this number should be reduced as module deployment increases.
Figure 12. Project cost estimates for new stream-reach hydropower developments in the United States
provided during the planning, engineering, and construction phases of project development.
(O’Connor et al. 2015)
A.4.5 Estimated Useful Life
Standard of measurement Target
How long a module is expected to remain
in operation before needing replacement
Employ fit-for-purpose, environmentally compatible module designs
that trade off cost, efficiency, durability, and modular replacement
Conventional hydropower plants can last over 100 years. The SMH strategy is to maximize the useful life
of modules, although fit-for-purpose, environmentally compatible module designs are expected to trade
off cost, efficiency, durability, and modular replacement to improve deployment opportunities. When
designed in this way, a generation module, on average, may fail more frequently than conventional
designs, although it can be replaced inexpensively without jeopardizing public or worker safety as a result
of catastrophic failure and without severe facility performance degradation. Ultimately, this trade-off
must be explored in depth through techno-economic cost models.
A.4.6 Maintainability
Standard of measurement Target
How many man-hours does it take for
routine average maintenance
Minimize the need to remove nonessential equipment during repairs
and enable complete removal of a module from the foundation
module in a single day
A-21
Maintainability is determined by the complexity of the module and the specific module design. An
exemplary design will reduce module complexity so that isolated repairs can be made on individual
components. Project downtime can be minimized if a module can be easily removed without the need to
dewater or dismantle auxiliary equipment and systems. Several state-of-the art turbines can be lifted out
of a bay and replaced or repaired in one day.
A.5 DESIGN CONSTRAINTS
Generation module design constraints describe limitations on how the module must operate, restrictions
on what the module must produce, or conditions that must be met for an effective generation module
design (Table 5). These limitations and conditions are derived by considering the current small, low-head
hydropower potential in the United States as outlined in the MYRP, and the desired characteristics of an
exemplary generation module. They bound the design of modules to ensure environmentally conscious
decisions are incorporated into the development of new technologies. The design constraints are
characterized as “local” when they pertain specifically to the generation module and “global” when their
validity can be extended to the other modules of the SMH facility.
Table 5. GM design constraints
Constraint Formalization/rationale
Scale
(L= local
G = global)
Must be run-of-river and operate
within natural variations of head
and flow
To minimize environmental disturbances at a site, an
SMH facility cannot appreciably alter the quantity,
timing, or duration of natural flow regimes. This
constraint requires the generation module to operate as
run-or-river, meaning the sum of inflows into the
upstream region of the facility must equal the sum of
outflows into the downstream reach of the facility
L, G
Must maintain safe operation of
equipment and systems within the
generation module during all
operational scenarios (normal
operations, flood, drought, special
hydraulic operations, emergency
shutdown, startup, and ramping up
and down)
The generation module is fixed instream and will
encounter both design and off-design conditions during
normal conditions and during extreme events. The
module itself must include all equipment and systems to
guarantee safe operation under all expected conditions; to
ensure public health and safety are not at risk; and to
protect the module from water, electrical, and structural
damage
G
Must produce 3-phase power at
60 Hz
The US power system operates at a frequency of 60 Hz.
This constraint has implications for the rotational speed
of the runner and generator, which must either
independently, via a mechanical speed increaser, or
deliver electricity at the appropriate frequency through
power electronics
L
Must accommodate heads of less
than 30 ft and flows less than
4,000 cfs
The US new stream-reach hydropower development
potential addressed through SMH research is broadly
characterized as low-head and low power. To accommodate
a large majority of these sites, a generation module must
operate under a maximum head and flow limit
L, G
Must not appreciably increase the
temperature of water as it moves
through the module
Some generators (e.g., those encapsulated in bulb type
turbines) may rely on the flow of water through the
module to dissipate heat from generation. The thermal
regime of the river is an important water quality
characteristic that cannot be altered appreciably from the
natural state
L
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Table 5. GM design constraints (continued)
Constraint Formalization/rationale
Scale
(L= local
G = global)
Must use biodegradable oil and
lubricants or water-lubricated
bearings
A generation module may require the use of oil or
lubricants in hydraulic systems that regulate gate openings,
turn blades or guide vanes, or lubricate bearings. These oils
and lubricants cannot be released into the flow. The use of
water-lubricated bearings or biodegradable oil and
lubricants is preferred
L
Cannot kill or injure fish
Traditional approaches to downstream fish passage either
exclude fish from turbines with screens or racks at the
intake, or allow them to pass through the turbines. If fish
are excluded from the intake they must be provided with
another means of downstream transport, either through a
dedicated passage facility or through a trap and truck
approach. Allowing fish to pass through the turbine
requires additional constraints on turbine design to
account for the effects of rapid pressure fluctuations,
blade strikes, shear stresses, mechanical grinding,
cavitation, and turbulence on fish survivability. This
constraint also requires consideration of fish attracted to
the outflow of water from the module that may try and
swim up through the module
L
Must not be excessively loud
Loud hydropower plants are audibly disruptive to the
surrounding environment and socially unacceptable. The
generation module must remain within acceptable limits
of noise
L
Must conform with all relevant
standards and codes for hydropower
generators
Standards and codes applicable to hydraulic turbines and
generators must be met, including ANSI, IEEE, and
NERC specifications relating to the acceptance of new
electrical equipment and apparatus
L
ANSI = American National Standards Institute; IEEE = Institute of Electrical and Electronics Engineers; NERC = North
American Electric Reliability Corporation.
A.6 DESIGN ENVELOPE SPECIFICATION
To fully tap into the potential of small hydropower, development of a compact fit-for-purpose turbine
runner and generator— a generation module—is crucial. The generation module is envisioned as a
hydropower generation technology that spans 100 kW—2 MW of power generation (per turbine) and is
designed based on cost effective run-of-river designs that eliminate the need for dam storage or employ
only a small barrage to create a low head. The requirements, constraints, and measures of performance
laid out above are intended to create a bounded envelope for generation module design innovation. Their
implications can be summarized as follows:
A generation module must receive upstream flows at an intake, pass them through the module, and
discharge them downstream.
It is anticipated that the generation modules will be fully immersed in water, which necessitates the
use of a reaction-type turbine design in which the runner blades are profiled to create a lift force and
generate torque based on the principle of a “propeller” that runs in reverse.
A generation module must encompass all equipment and systems for safe and reliable water power
generation.
A-23
The generation module should accommodate design flows of less than 4,000 cfs per unit and design
heads of less than 30 ft per unit.
Run-of-river type operation is expected, with a generation module operating within the natural
variation of head and flow.
The module must minimize environmental disturbance—it cannot kill or injure fish, release oil or
lubricants into the flow, appreciably increase the temperature of water, or emit loud and obtrusive
noise during operation.
Design decisions—including type of turbine, type of generator, mechanical turbine-generator
coupling, turbine-generator configuration, number of turbine runner blades, speed control system, and
necessary peripheral equipment—are to be determined by individual generation module manufacturers
with consideration of the requirements, constraints, and measures of performance outlined herein.
Many of these specifications are met by existing technologies, although the concept of a fit-to-purpose
generation module that incorporates all specifications and conforms to the SMH facility concept is new.
A.6.1 State-of-the-Art Advances
Advanced small hydropower designs have been identified that embody exemplary characteristics and
improve the generation module conception. There is high uncertainty with respect to their cost, as most
solutions are proprietary and detailed cost data are not provided. Thus, it is unclear if their inclusion in a
generation module design will improve the overall feasibility of the SMH concept. However, they are
briefly described here to further characterize an exemplary generation module.
A.6.1.1 Variable-speed power electronics coupled with permanent magnet generators
A recent US Department of Energy–funded project (Kinloch 2015) replaced an induction generator at a
low-head small hydropower site with a variable-speed drive (VSD) and a PMG. A VSD and PMG use
one power converter box to adjust the output voltage and frequency of the generator, allowing the turbine
to spin at the optimum speed for the given input hydraulic power. This technology eliminates the need for
a contactor, exciter, voltage regulator, auto-synchronizer, speed increaser, and speed-matching controls.
The system is considered off-the-shelf, as it is already in use for wind turbines.
The original fixed-blade runner and supporting civil works were left intact, allowing for an exact
performance improvement evaluation of the new generator and power electronics. The new technology
resulted in reduced complexity and fewer components than the existing induction generator (and a
comparable synchronous generator), and is expected to produce 96% more energy per year than the
previous generator system. The major improvements came from (1) operating the fixed-blade turbine at
optimum speed over a full range of head and (2) operating the turbine at optimum speed at the maximum
design head (as the old induction system was unintentionally mismatched and the generator was running
at a speed that was too high, resulting in poor performance). The overall improvement in real power and
efficiency over a range of heads is shown in Figure 13 and Figure 14, respectively. Although the project
principal investigator stated it is not possible to isolate the performance improvements due solely to the
VSD and PMG system (i.e., due to the technology and not to correcting the turbine-generator speed
mismatch), it is clear that coupled VSD and PMG technologies reduce complexity, increase flexibility,
enable more compact designs, and have the potential to improve efficiency over a wide range of heads
and flows.
The cost of equipment and supplies for the project totaled $64,105, or $2,331/kW based on the roughly
27 kW output at the approximate design head of 8.55 ft, with an estimated payback period of roughly 7
years. The power output of this site is fairly low, although the concept can be applied at larger sites; and
the principal investigator suggests this technology applied on larger streams with more variation in head
A-24
would see increased benefits. The VSD technology can also be added without a PMG at roughly half the
cost of the current project. This approach would also yield benefits for a module designed with a
conventional generator.
Figure 13. Average power output of the new VSD and PMG system compared with the former induction
generator. (Kinloch 2015)
Figure 14. Net real power efficiency of the new VSD and PMG system compared with the
former induction generator. (Kinloch 2015)
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A.6.1.2 Fully submersible turbine and generator assembly
A fully submersible generation module incorporating the entire turbine and generator assembly into a
single compact design has been introduced in the past several years. One recent example is the Amjet
Turbine5 (Figure 15), a 5 ft long and 8 ft wide rim-rotor hydropower turbine unit. The unit uses variable-
speed technology and a PMG to eliminate the need for mechanical controls. It can operate at multiple
power ranges to match varying heads; a composite turbine housing reduces overall unit weight; it can be
installed in-line at existing structures without the need for a foundation; and it includes only one rotating
part, the rotor, minimizing the overall footprint and complexity of interoperating components. Installation
design and Federal Energy Regulatory Commission approval are currently in progress. Other examples
include the Voith StreamDiver and the ANDRITZ HydroMatrix, bulb-type turbines that incorporate the
generator into a hub on the upstream nose of the unit.
Figure 15. Amjet Turbine Systems low-head turbine with embedded permanent magnet generator and
variable-speed electronic flow control that eliminates the need for conventional peripheral equipment. (Personal communication between S. DeNeale, Oak Ridge National Laboratory, and P. Roos, Amjet Turbine
Systems, LLC, March, 23, 2016)
An additional benefit of fully submersible units is they may eliminate the need for a conventional
powerhouse (Figure 16 and Figure 17). An acute issue at low-head sites is the volume of concrete
necessary for a powerhouse. Low-head turbines have larger diameters to accommodate higher discharges,
increasing the structural stability requirements. Incorporating the generation equipment and systems into a
fully submersible and compact unit can reduce the cost of civil works, the overall project complexity, and
project construction times.
5 http://amjethydro.com/
A-26
Figure 16. VLH turbine technology (right) eliminates powerhouse superstructure associated with more
conventional technologies (left). (Source: MJ2 Technologies North America. Used by permission.)
Figure 17. Installed unit (left) and cutaway sketch (right) of the Turbinator turbine-generator integrated
technology installed without a powerhouse. (Opsahl 2013)
A.6.2 Research Gaps
A.6.2.1 Techno-economic tradeoffs
All generation module design decisions have specific economic implications that challenge the inclusion
of exemplary technologies. New designs and technologies are more expensive when first introduced, and
they require adoption at scale before the economics become attractive. The biggest research unknown is
whether the costs of new exemplary designs can be competitive while ensuring favorable long-term
environmental and technical performance. Specific techno-economic tradeoffs to be researched include
Advanced flow control
Flow available for generation with respect to other module uses
A.6.2.2 Structural integration into a foundation module
The generation module is required to embed or anchor into the foundation module at a site. This concept
represents the largest departure from conventional thinking, and a current research gap with respect to
A-27
where and how these kinds of assemblies can be installed. The authors have identified two emerging low-
head hydropower technologies, the VLH turbine6 and the Ossberger movable powerhouse
7, which secure
an integrated runner and generator unit into place on top of a modular-type foundation structure. In both
cases, the foundation consists of two vertical parallel side-walls and a bottom foundation that is either
stepped (VLH) or sloped (Ossberger). Both units are inclined with respect to the bottom wall and do not
require a powerhouse, reducing the excavation required to secure the unit in place.
A.6.2.3 Module performance characteristics relative to traditional impoundment designs
To minimize the environmental footprint of hydropower operations and limit the disruption of flow
regimes, the generation module must operate without an impoundment, akin to conventional run-of-river
type operation. The extent to which a module design may be situated in a stream without any sort of
impoundment, or with a partial impoundment that leaves a portion of the stream undisturbed, is currently
unknown.
A.6.2.4 Use of advanced materials and manufacturing techniques in module design
The turbine runner is usually made of cast iron or steel, durable metals with high cycle fatigue and limited
susceptibility to cavitation, erosion, and corrosion. Modern composites have strength and stability
comparable to those of steel at a fraction of the total weight. A few emerging small hydro technologies
are incorporating carbon fiber materials in turbine runners and runner blades to produce lightweight,
modular, mass-producible designs. Applied research has shown that systematic assembly of composite
turbines could lead to reduced labor costs and substantial weight reductions (Whitehead and Albertani
2015). The use of thermoset plastics, sintered metals, and ceramic coatings is frequently proposed as a
target for small hydropower R&D, although these materials have yet to be incorporated into generation
technology on a large scale (Zhang et al. 2012). Although composite turbine blades are seeing increased
adoption in wind turbine designs and marine hydrokinetic installations, very little research has been
carried out on the performance or benefits of hydropower turbines fabricated with composite materials.
Additive manufacturing, or the 3-dimensional printing of components in layers, enables fabrication of
composite components with fewer bolted connections, reduced manufacturing labor costs, and higher
throughput. These features have led to significant cost reductions for mass-produced components in other
industrial sectors, namely pumps and pump impellers. A significant challenge to widespread use of this
technique is the relatively slow pace of small hydropower development in the United States.
A.6.2.5 Use of permanent magnet generators with non-rare earth materials
Although PMGs with rare earth magnets offer high torque/power density, alternatives with reduced or no
use of rare earth materials are possible. Alternative magnet types include AlNiCo, ferrite, and samarium
cobalt. AlNiCo and ferrite magnets, in particular, have a much smaller energy product than rare earth
permanent magnets. A lower energy product indicates lower magnet strength, which necessitates an
overall increase in magnet volume. This poses difficulties for the mechanical design of the rotor. Because
of their low coercivity, AlNiCo and ferrite magnets are more susceptible to demagnetization in a surface-
mounted configuration. The low remnant flux density of ferrite magnets makes it difficult, if not
impossible, for them to achieve power densities similar to those of that of a rare earth magnet, surface-
mounted PMG. Some of the difficulties of using low-cost magnets can be ameliorated by combining them
with the reluctance generator topology to increase the overall output. Reluctance generators can also
operate without magnets entirely, but they may be disadvantaged by a worse power factor.
6 http://www.vlh-turbine.com/
7 http://owa.ca/assets/files/presentations/FINALOssbergerPresentation.pdf
B-1
APPENDIX B. FISH PASSAGE MODULE
Hydropower facilities can work as total, partial, and/or permanent temporal barriers (Table 6) or a
combination of these with regard to the movement of native (anadromous, catadromous, amphidromous,
and residential) fish species (Larinier 2000; Schilt 2007; Noonan et al. 2012; Fuller et al. 2015). In
addition to being total, partial, or temporal barriers to fish movement, hydropower facilities often impair
the natural sense of direction of fish by creating low-flow-velocity regions, which are not natural to fish
(Cada 1997; Larinier 2000; Katopodis 1992). The disruption of the connectivity of fish movement
impedes fish lifecycles, including spawning/feeding purposes. In a nutshell, this disruption has impacts on
fish survival, mortality rates, health, biodiversity, and habitat.
Table 6. Classification of barriers with respect to fish movement (adapted from the California Department
of Fish and Game)
Barrier category Definition Potential impacts
Temporal Impassable to all fish at certain flow
conditions (based on run timing and
flow conditions)
Delay in movement beyond the
barrier for some period of time
Partial Impassable to some fish species
during part or all life stages at all
flows
Exclusion of certain species during
their life stages from portions of a
watershed
Total Impassable to all fish at all flows Exclusion of all species from
portions of a watershed
B.1 OBJECTIVES
To minimize the barriers posed by an SMH facility to migratory fish movement upstream and
downstream in a river, and thus preserve the connectivity of migratory fish population and habitat, the
SMH facility includes a fish passage module. The primary technical objective of the fish passage module
is to allow the unimpeded and safe passage (upstream or downstream) of fish through an SMH facility.
To succeed in its primary technical objective, the fish passage module must possess favorable geometry
and create hydraulic conditions such that fish are encouraged to cross the SMH facility in a safe manner
by minimizing fish fatigue, disorientation, and injury. These objectives are shown for both upstream and
downstream passage in Figure 18. A key prerequisite for the passage of fish across the SMH facility is
that fish must enter the fish passage module inlet. The modification of the natural river flow conditions by
the presence of the SMH facility causes fish disorientation, which could, in turn, prevent fish from finding
the fish passage module entrance that allows them to cross the facility. Thus, fish need to be guided
toward the module inlet before they can use the fish passage module. Although fish guidance is generally
required for both upstream and downstream fish passage, downstream fish passage may additionally
require minimizing the likelihood of fish entering the generation module. It is recognized that fish-
friendly turbine designs have recently been developed (Cada 2001; Pracheil et al. 2016) that limit fish
injury and achieve high survival rates of fish passing through the turbine (Ferguson et al. 2006). However,
the generation module is still considered the route that results in higher rates of fish injury, as well as
direct and indirect mortality, especially for adult fish (Cada 2001; Schilt 2007). Therefore, fish may need
to be deterred from entering the generation module of an SMH facility and guided to the fish passage
Fish Passage Module Primary Technical Objective
To allow the unimpeded and safe passage (upstream and downstream) of fish through a SMH facility
B-2
module, which ensures safe passage. Finally, the fish passage module outlet configuration must minimize
fish injuries and disorientation and allow fish to exit safely into the waterway to resume their migration.
Figure 18. Conceptual schematic of the specific objectives of a fish passage module. Note that downstream and
upstream passage of fish are shown together on the same module because of the shared requirements of attraction,
safe passage, and release, and their relationship to hydraulic conditions in and around the module. Separate upstream
and downstream passage modules may be required.
In summary, to achieve its primary objective, the fish passage module must accomplish the following
specific objectives:
1. Attract fish to the module inlet. Specifically for downstream fish passage, the fish passage module
should also deter fish from entering the generation module.
2. Allow fish to cross the SMH facility.
3. Allow fish to exit safely into the river (downstream or upstream) of the SMH facility.
4. Integrate structurally into the foundation module.
B.2 REQUIREMENTS
The requirements of the fish passage module are a series of quantifiable characteristics or behaviors that
the module must exhibit to accomplish each one of its specific objectives. In turn, by fulfilling its specific
objectives, the fish passage module will achieve its primary objective of allowing the unimpeded and safe
B-3
passage of fish across the SMH facility. Fish passage module requirements are presented in Table 7,
Table 8, and Table 9 and characterized as Functional, Performance, Interface and Other, based on the
following criteria:
Functional requirement: The requirement is a behavior or function that needs to be performed for
successful module operation.
Performance requirement: The requirement is quantified by how well a function is accomplished.
Interface requirement: The requirement involves interaction of the fish passage module with other
modules, e.g., water passage, generation.
Other: There is a lack of knowledge regarding the requirement at present.
Achieving the passage module requirements aims to minimize disruption of the connectivity in the river
continuum in terms of its five constituents: water, sediment, energy, organisms, and water quality. It is
therefore pertinent to identify the relationship(s) of each requirement of the fish passage module with one
or more of the environmental constituents, as indicated in the five rightmost columns of Table 7, Table 8,
and Table 9. Identifying these relationships further allows isolating interactions between the fish passage
module and other modules by considering the requirements of the various modules that relate to the same
constituent. Note that these requirements pertain to both upstream and downstream fish passage modules,
unless one of the two is specifically identified.
A key prerequisite for ensuring the passage of fish through the SMH facility, and thus accomplishing the
primary objective of the fish passage module, is to guide fish to the fish passage inlet (see Table 7). Fish
that cannot enter the fish passage module, which is the key conveyor of fish across the SMH facility, are
likely to become trapped upstream or downstream of the SMH facility (OTA 1995). Their entrapment not
only impedes their migration, thus disrupting fish connectivity along the river continuum, but also
increases fish exposure to predators and thus fish mortality rates (Larinier 2000; Schilt 2007). However,
detection of the fish passage module entrance by the fish is not straightforward. Previous research has
suggested that migratory fish possess complex biological mechanosensory systems that detect water
motion against their bodies (Coombs et al. 1989; Montgomery et al. 1997; Schilt 2007). Using water
motion to guide them, fish sense their direction of travel and avoid obstacles.
As a result, complex flow patterns—including regions of strong acceleration, deceleration, and
recirculation—in the vicinity of the fish passage module entrance are likely to disorient fish. A key
requirement for the fish passage module is to limit flow patterns unfavorable to fish movement (OTA
1995) and provide for a consistent flow stream that will guide fish toward the fish passage module
entrance. In addition, the flow depth near the fish passage module entrance must exceed a minimum
threshold to allow fish to swim (OTA 1995). The interaction of the approaching river flow typically leads
to elevated turbulence levels, through the creation of shear layers and mixing between slow and fast-
moving fluid in the river and in the fish passage, respectively. Elevated levels of turbulence may cause
disorientation and excessive fatigue to fish and therefore should be limited.
B-4
Table 7. Fish passage module functional requirements: objective 1—attract fish to the module. In the fourth
column: F = Functional; P = Performance; I = Interaction; O = other. In columns 6–11, an “X” denotes a
relationship to the river continuum constituent indicated in the top row
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter q
ua
lity
1
Attract fish to the module
inlet. Specifically for
downstream fish passage, the
fish passage module should
also deter fish from entering
the generation module (GM)
a
Maintain favorable flow
conditions and patterns at the
fish passage module inlet
F
The flow at the module
entrance should not exhibit
complex flow patterns that
disorient fish. Also a minimum
flow depth should be ensured.
Elevated levels of turbulence
should be avoided
X X
b
Guide fish to the passage
module inlet using behavioral
guidance (e.g., light, sound,
electricity) and/or barriers
(e.g., screens/walls/grates/
adjustable curtains)
F
The flow deceleration near the
hydropower facility causes fish
to lose their sense of travel
direction. Thus, fish should be
guided to find the passage
module inlet in order to use it
and cross the facility
X X
c
Deter fish from entering the
GM during downstream
passage using behavioral
guidance (e.g., light, sound,
electricity) and/or barriers
(e.g., screens/walls/grates/
adjustable curtains)
F, I
Entrainment of fish into the
GM intake during downstream
passage increases their chance
of injury and limits the GM
performance. Therefore, fish
need to be encouraged to avoid
the GM inlet. Fish entrainment
in the GM may be inevitable,
so acceptable performance
levels need to be set
X X
d Accomplish predetermined
fish attraction rates P
To preserve the continuity of
the fish species along the river,
a minimum number of fish
must enter the fish passage
module to pass it
X X
The deceleration of the river flow, particularly upstream but also downstream of an SMH facility, also
prevents fish from sensing the water flow and causes disorientation. To prevent fish disorientation and
encourage fish to enter the fish passage module, the module must feature guidance devices (Table 8).
There are two broad categories of guidance devices: barriers and behavioral guidance devices (Larinier
2000; Schilt 2007; CNRA 2013). Barriers include various types of fixed or movable screens (e.g., Eicher
screens, vertical and inclined fixed flat-plate screens), structures (e.g., angled and “louver” racks), as well
as movable barrier nets and curtains (OTA 1995; Schilt 2007; CNRA 2013). The barrier guidance devices
B-5
prevent fish from crossing them and allow fish to move only along their length, thus delineating a path for
fish movement. The fish passage module will need to include such barrier guidance devices to delineate a
path that guides fish to the module entrance. Behavioral attraction devices, on the other hand, use stimuli
such as light, sound, or turbulence to generate fish movement toward or away the devices. However, these
behavioral attraction devices are relatively new technologies; to date, they have seen limited testing and
application and should be used with caution in the fish passage module (Schilt 2007 CNRA 2013). Note
the requirement of attracting fish to the fish passage module inlet is common for both downstream and
upstream passage, to allow crossing of the SMH facility by catadromous and anadromous fish,
respectively.
An additional requirement for downstream migrating fish is that the fish passage module must discourage
the entrainment of fish into the inlet of the generation module. Despite improvements made in the design
of turbines to make them more fish-friendly and improve the survival chances of fish entrained through
the turbines, passage of fish through the turbines is the least safe passage or escape route with the highest
chances of fish injury (Cada 2001; Schilt 2007). Further, the increased pressure and turbulence generated
in the generation module turbines could disorient fish, which has implications for fish mortality (Cada
2001; Schilt 2007). To minimize the likelihood of fish entrainment into the generation module, the fish
passage module may need to employ fish guidance devices (barriers or behavioral guidance devices such
as curtains) that direct downstream migrating fish away from the generation module and into the fish
passage module.
Finally, the fish passage module must achieve a predetermined minimum rate of fish attraction to its inlet.
The fish attraction rate is typically quantified by the ratio of migrating fish entering the fish passage
module to the total number of migrating fish (Roscoe and Hinch 2010; Cooke and Hinch 2013).
Satisfying a minimum fish attraction rate to the fish inlet ensures that a minimum number of migrating
fish will use the fish passage module and eventually pass through the SMH facility, thus minimizing the
disruption caused by the SMH facility to the continuity of existing fish species in the river. The minimum
threshold for fish attraction rate needs to be determined based on an assessment of the specific river
conditions and thus is a measure of the fish passage module performance, as will be discussed in detail in
Appendix B.4.
Perhaps the most important specific objective/utility of the fish passage module is to allow downstream
and upstream migrating fish to safely and consistently cross the SMH facility. To do so, a portion of the
river flow must be diverted into the fish passage module, and the portion of the flow routed through the
fish passage module should be kept within relatively well-defined bounds even under changing
hydrologic conditions for the river. To retain the diverted flow within the fish passage module within this
predetermined range, it is necessary for the fish passage module to interface with the water passage
module. This interface can make provisions for directing additional water volume to the fish passage
module at low-flow conditions and for excess water removal during flood conditions, so that favorable
conditions for fish movement are sustained within the fish passage module.
B-6
Table 8. Fish passage module functional requirements: objective 2—allow fish to cross SMH facility. In the
fourth column: F = Functional; P = Performance; I = Interaction; O = other. In columns 6–10, an “X” denotes a
relationship to the river continuum constituent indicated in the top row
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter q
ua
lity
2 Allow fish to cross the
SMH facility
a Divert a sufficient
portion of the river
flow
F, I, O
A portion of the river flow should be
diverted in the passage module to allow fish
to swim in the passage. This portion is thus
not used by the generation module and must
be supplied by the water passage module
X X
b Sustain appropriate
flow conditions and
flow patterns
F
Fish require flow velocities below a
threshold to prevent excessive fatigue—
especially for upstream passage, a minimum
flow depth to be able to swim, and low-flow-
velocity resting regions. Also, turbulence
levels must be retained below a threshold.
These thresholds are specific to fish species
and age
X X X
c
Retain
passage/structure
dimensions to levels
manageable by the fish
F, P
The fish passage structure elements (e.g.,
baffles, steps) need to be smaller than the
fish jump height to allow fish crossing. Also,
the passage structure length should be as
short as possible to minimize fish fatigue
during crossing
X X
d Guide fish toward the
module exit F
Fish may lose their sense of direction in an
artificial passage structure and be unable to
swim toward its exit X X
e Prevent excessive
sediment accumulation
in the passage
F, P
Excessive sediment deposition in the passage
module may alter its flow patterns, thus
reducing its efficiency in passing fish
X X X
f
Maintain dissolved
oxygen and bubble
entrainment within
levels manageable by
fish
F, P
Excessive turbulence generated in the
structures may lead to increased dissolved
oxygen levels and/or bubble entrainment,
which impair fish health
X X X
Sustaining favorable conditions within the fish passage module entails ensuring that mean flow patterns
are favorable to fish, without regions of weak or strong flow acceleration, deceleration, and swirling
motion (Table 9). Favorable flow conditions within the fish passage module further entail sustaining a
minimum flow depth so that the encountered migrating fish species are able to swim. Furthermore, the
flow velocity within the fish passage module must be retained below thresholds manageable by the fish
that encounter it (Katopodis 1992; OTA 1995; Larinier 2000; Dermisis and Papanicolaou 2009; CNRA
2013). If not, strong currents will lead to excessive fish fatigue and injury, thereby preventing fish from
safely crossing the SMH facility. This is particularly relevant to upstream fish passage, where fish swim
against the flow direction and must therefore exert a larger effort to overcome higher flow velocities.
Also, the turbulence within the fish passage module should be maintained below certain limits, as
excessive turbulence increases fish fatigue and the probability that fish become disoriented.
B-7
An additional requirement for the fish passage module (Table 9) is that its geometry is manageable by the
fish species encountered in the stream. This requirement, which is more important for upstream migrating
fish, entails that the height of the fish passage module elements—including steps, baffles and weirs—be
within the jumping ability of the prevalent fish species encountered. If not, these elements will become a
permanent barrier to fish, making the SMH facility impassable to them. In addition, the fish passage
module geometry should minimize areas with intense flow acceleration, deceleration, and recirculation, as
well as areas with pronounced turbulence, such as shear layers and downwelling. Overall the fish passage
module geometry should contribute to maintaining favorable flow conditions for fish. The length of the
fish passage module must be kept as short as possible so that delays in fish migration through the SMH
facility are minimized. At the same time, however, the fish passage module should not be too steep and
must not cause high flow velocities within the passage.
The complex flow patterns within the fish passage module may disorient fish, which base their orientation
on their interaction with the flow (Coombs et al. 1989; Montgomery et al. 1997; Schilt 2007). To prevent
fish disorientation within the fish passage, which could lead to delays in fish migration, fatigue, and
injury, the fish passage module needs to feature barriers or behavioral guidance devices for ensuring that
fish find the exit.
Especially at higher flows, river sediment may be entrained into the fish passage module (OTA 1995).
Because the flow within the fish passage decelerates to maintain flow conditions manageable by fish,
incoming sediment could deposit within the fish passage module. Sediment accumulation could alter the
geometric characteristics of the fish passage module and, in turn, the flow characteristics in the module.
For instance, sediment deposition could reduce the flow depth, creating shallow but fast flow regions that
are not manageable by fish. To prevent sediment accumulation within the module, the flow conditions in
the fish passage module should be competent to transport the sediment material supplied from upstream.
Finally, increased turbulence resulting from the interaction of the incoming flow with the fish passage
structure can lead to excessive air bubble entrainment in the flow (Chanson 2009). Elevated levels of air
bubbles are known to cause “gas bubble trauma” to fish, which can ultimately lead to fish death (OTA
1995). Enhanced air entrainment also causes fish to become disoriented. To prevent such a condition, the
fish passage module must minimize turbulence production and gas bubble entrainment into the flow.
At its exit, the fish passage module should exhibit characteristics that allow the safe exit of the fish into
the river (Table 9). A key prerequisite for safe exit from both the upstream and downstream passage is to
maintain flow conditions and patterns that prevent fish from being disoriented. At the exit of the
downstream passage, enhanced turbulence from the mixing of the water moving in the fish passage with
the low-speed water downstream of an SMH facility can result in increased turbulence levels and
recirculating patterns that disorient the exiting fish, therefore effectively trapping them near the exit. As
upstream-migrating fish exit the upstream passage, they can experience nearly stagnant water upstream of
the SMH facility, which could also disorient them. Therefore, for both downstream and upstream passage,
the flow conditions should neither delay fish migration downstream nor increase indirect fish mortality
from predators (OTA 1995; Cada 2001; CNRA 2013). The maintenance of flow conditions that minimize
fish disorientation at the fish passage module exit should be complemented with guidance devices.
Specifically for downstream passage, the exit of the fish passage module must not be located at a much
higher elevation than the water surface.
B-8
Table 9. Fish passage module functional requirements; objective 3—allow fish to exit safely into the stream.
In the fourth column: F = Functional; P = Performance; I = Interaction; O = other. In columns 6–10, an “X” denotes
a relationship to the river continuum constituent indicated in the top row
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter q
ua
lity
3 Allow fish to exit safely into
the river
a
Minimize fish disorientation
from mean flow and
turbulence
F, I, O
The enhanced turbulence and
exit flow patterns may
disorient fish, effectively
trapping them in the vicinity of
the hydropower facility
X X
b Retain exit structure height
to levels manageable by fish F, P
The fish passage outlet
structures should not allow
fish to drop or jump more than
their jumping height
X X X
c
Keep air bubble entrainment
within levels manageable by
fish
F, P, I
Flows plunging into the river
at the passage module exit
could lead to increased air
bubble entrainment, which can
disorient fish exiting the
facility
X X X
d Accomplish predetermined
fish passage rates P
To preserve the continuity of
the fish species along the river,
a minimum number of fish
must enter the passage module
to pass it safely
X
4 Integrate structurally into
foundation module
a
Transmit all forces through
non-critical components into
the foundation module
F, P, I
The fish passage module will
be supported instream by a
foundation module that serves
as an interface to the
streambed
X
Finally, the fish passage module must achieve predetermined fish passage rates to preserve the continuity
of the fish species in the river on which the SMH is located. The fish passage rates will need to be
determined a priori following an assessment of the SMH site characteristics at different scales; this
process will be discussed in more detail in Appendices B.4 and B.5.
B.3 INPUTS, PROCESSES, FUNCTIONAL RELATIONSHIPS
In this section, we identify the key processes that govern the operation of the fish passage module. These
processes, and the functional relationships that quantify them, are important for understanding the
function and predicting the behavior of the fish passage module. This understanding will, in turn, allow
design of the fish passage module in a way that effectively minimizes disruption of the connectivity of
fish along the river continuum that the SMH facility may cause under a variety of flow conditions. Before
B-9
identifying these processes, however, it is pertinent to isolate the key variables that are the inputs to these
relationships.
B.3.1 Necessary Inputs
The key inputs (or variables) relevant to the fish passage module concept are presented in Table 10. These
key inputs are grouped in five categories, depending on how they relate to biological, flow, geometric,
geomorphologic, or chemical processes. This categorization allows a systematic examination of the
functional relationships to which these inputs relate, as is discussed in Appendix B.3.2.
Table 10. Key inputs for the function of the fish passage module
Identification of
key inputs Formalization
Fish species and accompanying
biological characteristics
Species type, fish length, endurance, jump height, swimming speed,
fish age
Flow variables
Range of flow discharges encountered, watershed hydrologic
characteristics, flow depth, turbulence kinetic energy, turbulence
dissipation, characteristic eddy length, water temperature, friction
factor
Geometric variables
Type of passage module, elevation difference upstream and
downstream of facility, passage module slope, passage module length,
passage module width, passage module element (e.g., baffle, weir,
step/pool) height
Geomorphologic variables Grain size distribution, friction factor, sediment fall velocity, sediment
characteristics (shape, angularity)
B.3.2 Functional Relationships
The functional relationships that govern the transport processes relating to the fish passage module are
summarized in Table 11, along with brief descriptions of their importance. The first category involves the
functional relationships among the fish biological variables. In this category is fish swimming speed
(velocity), which depends on the fish species and age (Figure 19). More specifically, past work on fish
swimming speed has shown that three types of fish swimming speeds can be identified: cruising,
sustained, and darting (NRCS 2007; Meixler et al. 2009). Cruising speed, the slowest of the three, is the
swimming speed at which a fish can travel for time periods longer than 1 hour. Sustained speed is the
velocity at which a fish can travel for time periods between 1 minute and 1 hour. Darting speed, the
fastest of the three velocities, is the velocity at which a fish can swim for time periods of less than
1 minute. The three types of fish velocities are specific to the fish species; larger fish, such as salmon, are
capable of achieving higher cruising and sustained speeds (Figure 19). In addition, age significantly
affects the swimming speeds of the various species. Typically, juvenile fish can achieve lower cruising
and sustained speeds than adult fish of the same species. More important, juvenile fish may not be
sufficiently developed to be capable of darting speeds, which becomes an important issue when fish are
using the fish passage module.
Table 11. Functional relationships governing fish passage module operation
Relationship of To Rationale/importance
Fish swimming
speed
Fish species and age The swimming speed that a fish can achieve depends on the fish
species and age, i.e., whether it is an adult or juvenile individual
Fish length Fish species and age The different lengths (sizes) of various fish species relate to the
sizes of the turbulent eddies that fish can overcome
B-10
Table 11. Functional relationships governing fish passage module operation (continued)
Relationship of To Rationale/importance
Fish endurance
Fish species,
swimming speed,
water temperature
The endurance of fish relates to their swimming velocity, species,
and age
Fish jump height Fish species, water
temperature
The passage cannot have obstacles with heights exceeding the
jumping height of the target fish species
Flow velocity in fish
passage
Discharge, passage
geometry, passage
roughness, flow
depth
Flow velocities higher than the fish swimming speed cause
excessive fatigue and disorientation in fish
Flow depth in fish
passage
Discharge, passage
geometry, passage
roughness, passage
bed slope
A minimum flow depth is required for each species to be able to
swim, which relates to the fish species
Turbulence
production and
dissipation
Discharge, passage
roughness, passage
configuration/type
Excessive turbulent kinetic energy levels may cause fish
displacement and disorientation. Increases in turbulence
dissipation are sought
Turbulence eddy
length scale
Discharge, passage
geometry, passage
roughness
Fish can tackle eddies with characteristic sizes comparable to or
smaller to their length. Hence, smaller eddies allow smaller fish
(e.g., juveniles) to pass
Sediment transport
Depth, slope,
friction, size
distribution of
transported material
Sediment may be entrained into the passage module. In that case,
its deposition must be prevented, especially at lower-flow
conditions
Figure 19. Swimming speeds for various species of fish: (left) adult individuals, (right) juvenile individuals.
(NRCS 2007)
B-11
The average fish length—the length between the fish nose and the base of the tail—is also dependent on
the fish species and age (Figure 20). Previous research (Papanicolaou and Maxwell 2000; Dermisis and
Papanicolaou 2009) has shown that fish can withstand only those turbulent eddies that are smaller in size
than their length, known also as fork length. Therefore, knowledge of the fish length for a species and the
age of the fish encountered at the SMH site can determine the suitability of the fish passage in terms of
turbulence characteristics.
The endurance of fish is defined as the time that a fish individually can swim at a given speed (Katopodis
1992; Ficke et al. 2011). Fish endurance is predominantly a function of the fish species, which in turn
determines the type of motion (mode) that the fish makes as it swims (Katopodis 1992; Ficke et al. 2011;
Meixler et al. 2009). As illustrated in Figure 20, fish endurance drops abruptly as the fish swimming
velocity increases. In other words, fish can swim fast only for limited periods of time. The endurance and
swimming speed can vary substantially among fish species. For instance, Figure 20 shows that brassy
minnows can swim almost twice as fast as Arkansas darters for time periods of less than 1 minute. Also,
water temperature can have significant impact on the swimming ability of certain fish species. As Figure
20 shows, a drop in the water temperature of 7.5C (14F) can lead to a tenfold drop in swimming
velocity. Note that the product of fish endurance and swimming velocity, i.e., the area under each
endurance-swimming velocity curve (Figure 20), yields the maximum distance that a fish can swim
before needing to rest.
Figure 20. Fish endurance (vertical axis) as function of fish swimming speed (horizontal axis) for different
fish species and water temperatures (after Ficke et al. 2011). (Reprinted by permission of Taylor & Francis Lt.
http://tandfonline.com)
In addition to the fish swimming velocity and endurance, another key characteristic that varies among
different fish species is their jumping height (Table 12). As noted in Appendix B.2, the various structural
elements, such as baffles, weirs and steps, of the fish passage module must be smaller than the fish
jumping height to make them passable by fish. Therefore, knowledge of the jumping height for fish
species is necessary for proper design of the fish passage module. Some research also suggests that the
jumping height for a given fish species depends on the water temperature (Ficke et al. 2011). Specifically,
a decrease in water temperature was found to cause a decrease in the fish jumping height, with extreme
reductions in water temperature causing fish not to jump.
The two main characteristics of the flow in the fish passage module are flow velocity and depth. These
two parameters, which are interrelated, are in general expressed as a function of the discharge flowing
into the fish passage module, the fish passage module geometry and bed slope, and the fish passage
module roughness (Chaudhry 2008). The discharge itself is a function of the drainage area of the
watershed in which the SMH facility is located, and of watershed characteristics such as land use and land
cover, soil type, and climatic conditions (Maidment 1993; Papanicolaou and Abban 2016). These
dependencies are examined in more detail in Appendix E, which discusses the water passage module.
B-12
Table 12. Key physiological characteristics for common freshwater fish species (Meixler et al. 2009).
(Obtained from Creative Commons under license CC BY-NC-ND 4.0
https://creativecommons.org/licenses/by-nc-nd/4.0/)
Common name Scientific name Maximum jumping
height (m)
Maximum darting
speed (m/s)
Average total length
(m) Migratory season
Alewife Alosa pseudohar engus 0.39 2.77 0.31 Spring
Alantic salmon Salmo salar 1.94 6.17 0.69 Fall
Brook trout Salveltnus fontinalls 0.37 2.70 0.30 Fall
Brown trout Salmo trutta 1.10 4.64 0.52 Fall
Chinook salmon Oncarhynchus tshawytsch
3.67 8.48 0.94 Summary
Coho salmon Oncarhynchus klsutch 1.47 5.36 0.60 Fall
Creek chubsucker Erimyzon oblongus 0.23 2.13 0.24 Springa
Fantail darter Etheostoma flaberllare 0.01 0.47 0.05 Spring
Gizzard shad Darosoma cepedianum 0.34 2.59 0.29 Spring
Iowa darter Etheostoma exile 0.01 0.49 0.05 Spring
Johnny darter Etheostoma nigrum 0.01 0.39 0.04 Spring
Northern hog sucker Hypenteltum nigricans 0.37 2.68 0.30 Spring
Northern pike Esox luctus 1.49 5.40 0.60 Spring
Shorthead redhorse Maxostoma macrolepidotum
0.57 3.36 0.37 Spring
Smallmouth bass Micropterus dolomieu 0.60 3.42 0.38 Spring
Spottail shiner Notropis hudsonius 0.04 0.85 0.09 Summer
Steelhead Rainbow trout 1.03 4.50 0.50 Spring
Walleye Sander vitreus 1.21 4.86 0.54 Spring
White perch Morone americana 0.0.09 1.36 0.15 Spring
White sucker Catostomus commer
sonill
0.68 3.66 0.41 Spring
Yellow perch Perca flavescens 0.22 2.06 0.23 Spring
Note, however, that the complex interactions between watershed characteristics and climate can cause
significant variability in the flow discharge at the SMH facility over time. This would lead to variability
in the flow discharge entering the fish passage module.
For typical types of fish passage, empirical relationships expressing the dependencies of flow velocity and
depth parameters upon discharge, fish passage module geometry, and slope have been developed
(Katopodis 1992). Experimental work has shown that the flow discharge expressed in dimensionless form
is related to the dimensionless flow depth in a linear fashion for different types of fish passage modules
(Figure 21). Considering the discharge and the flow depth in dimensionless form allows scaling of these
relationships between experiment and prototype, while also accounting for the bed slope effects on
discharge. Different fish passage module geometries (Figure 22) yield different slopes in the curves
relating the discharge and the flow depth (Figure 21).
Similar relationships have been developed for predicting the flow velocity from the flow discharge in the
fish passage module, as indicated in Figure 23. In this case, a power relationship between the flow
velocity and the discharge was determined (Figure 23). The bed surface roughness may also affect the
flow velocity and depth in the fish passage module (Chaudhry 2008). Its role is not as critical in artificial
structures that are made of concrete and have rather smooth surfaces, but roughness may become
important in nature-like fish passage modules with beds consisting of river sediment. In such cases, the
increased bed roughness causes a larger energy loss in the approach flow and decelerates the flow
velocity in the fish passage module. The flow velocity deceleration is larger as the roughness increases,
which is positively related to the size of the bed material.
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Figure 21. Relationship between the flow discharge, bed slope, and flow depth (Katopodis 1992). (Credit:
Chris Katopodis, P. Eng. Freshwater Institute: Central and Artic Region)8
Figure 22. Geometries of different fish passage modules and the expected flow patterns. (Katopodis 1992).
(Credit: Chris Katopodis, P. Eng. Freshwater Institute: Central and Artic Region)9
8 This reproduction is a copy of an official work that is published and owned by the Government of Canada and has
not been produced in affiliation with, or with the endorsement of the Government of Canada. 9 This reproduction is a copy of an official work that is published and owned by the Government of Canada and has
not been produced in affiliation with, or with the endorsement of the Government of Canada.
B-14
Figure 23. Relationship between the flow velocity (vertical axis) and discharge (horizontal axis) in the fish
passage module (Katopodis 1992). (Credit: Chris Katopodis, P. Eng. Freshwater Institute: Central and
Arctic Region)9
Note that the empirical relationships between velocity and flow discharge in the fish passage module
predict a characteristic or average velocity within the passage module. Such relationships, however, do
not provide an insight into the flow patterns within the fish passage module. The flow patterns in the
module may become complex, with adverse consequences for fish orientation (Puertas et al. 2004; Liu et
al. 2006; Tarrade et al. 2008; Wang et al. 2010; Marriner et al. 2014). As illustrated in the left panels of
Figure 24, the fish passage module geometry can have a profound impact on the flow patterns, creating
regions of high- and low-velocity fluid as well as recirculating flow. These flow features can lead to fish
disorientation and excessive fatigue and will need to be minimized (OTA 1995).
Turbulence is another phenomenon that plays a key role in the hydraulics of the fish passage module. The
level of turbulence is often quantified by the turbulent kinetic energy (TKE), with higher TKE indicating
more turbulent flow. In general, the interaction of high-speed fluid with low-speed fluid, or the interaction
of fluid with structures, leads to elevated levels of turbulence and higher TKE. For instance, turbulence is
elevated at the entrances of fish passage modules (Figure 24), where the flow streamlines are constricted
and high-speed fluid, represented by the darker regions in the center panels of Figure 24, interacts with
low-speed fluid, represented with the lighter colors in the center panels of Figure 24.
At the same time, the fluid turbulence is dissipated by the friction of the fluid with the bed and among the
fluid particles themselves. The dissipation of turbulence is quantified in an average sense over the volume
of the fish passage module by the energy dissipation function (EDF) (Liu et al. 2006; Wang et al. 2010). It
has been shown that the EDF is related to the flow discharge in the fish passage module, the slope of the
module, and its plan view geometry, i.e., its length and width (Liu et al. 2006; Tarrade et al. 2008).
Alternately, it has been shown that the EDF is a function of the velocity in the fish passage module and its
length (Wang et al. 2010). The turbulent dissipation and hence EDF is related to the characteristic
turbulent eddy length scales (Liu et al. 2006; Marriner et al. 2014). Therefore, some studies consider the
turbulent eddy length scales, in place of the EDF, as comparison of the characteristic eddy length scale
with the fish length offers a direct assessment of the suitability of a fish passage module in terms of
turbulence (Papanicolaou and Maxwell 2000; Liu et al. 2006; Dermisis and Papanicolaou 2009).
B-15
Figure 24. Flow patterns in fish passage modules of different geometry. The left panels illustrate the flow
streamlines, the center panels the velocity magnitude, and the right panels the turbulent kinetic energy (TKE) within
the fish passage module. Darker gray shades represent higher magnitudes of velocity and TKE. The top and bottom
rows correspond to fish passage modules with bed slopes of 5 and 15%, respectively. Flow enters from the bottom
left and exits at the bottom right of each panel. (Tarrade et al. 2008; Copyright: Springer Science+Business Media
BV and FAO 2008; With permission of Springer)
Although an SMH facility might have a devoted sediment passage module, it is possible that sediment
may enter into the fish passage module (OTA 1995). It is pertinent, therefore, to examine the key
functional relationships that govern the transport of sediment, to the extent that they relate to sediment
transported and deposited within the fish passage module. In general, coarser sediment that is transported
in proximity to the bed is deposited when the flow transport capacity is smaller and the sediment supply
from upstream exceeds the flow transport capacity (Yalin 1977). The sediment transport capacity is
typically expressed as a function of the difference between the force applied by the flow and the threshold
force that is required to set a coarse sediment grain of given size in motion (Yalin 1977). The applied flow
force, also termed the “bed shear stress,” is a function of the flow depth, the slope of the fish passage
module bed, and the density and size of the sediment grains to be transported. The threshold stress, also
known as the “critical bed shear stress for incipient motion,” is broadly dependent on the heterogeneity of
the bed material grains, their packing density, their shape, and their degree of protrusion into the flow
(Yalin 1977; Wiberg and Smith 1987; Papanicolaou et al. 2002). On the other hand, finer sediment is
typically transported in suspension. The suspended sediment is considered to settle out of suspension and
deposit when a characteristic velocity length scale of the flow, termed the “friction velocity” is less than
the settling velocity of the suspended sediment. The flow shear velocity is dependent on the flow depth
and bed slope, whereas the fall velocity is determined from the sediment size and water temperature
B-16
(Raudkivi 1998). These relationships inform fish passage module design, though if significant sediment
issues are observed at a site they should be addressed with a sediment passage module.
B.4 MEASURES OF MODULE PERFORMANCE
Assessing the efficiency of the fish passage module in meeting the requirements listed in Appendix B.2
requires a set of quantifiable indices. Such indices will allow, in turn, evaluation of the efficiency with
which the fish passage module accomplishes its specific and primary technical objectives.
To assess the performance of the fish passage module in terms of its primary technical objective of
consistently and safely passing fish across an SMH facility, a key index is the fish passage rate, which
indicates the proportion of fish (Table 13) that safely pass the SMH facility (Noonan et al. 2012). In
addition, it is necessary to know the survival rate of the fish that do not pass through the module to
identify features of the fish passage module or the flow patterns that contribute to fish mortality (Larinier
2000; CNRA 2013). The fish survival rate can be a useful index for assessing causes of indirect mortality
once fish have passed the SMH facility as well, e.g., from predation of disoriented fish. Examination of
the passage rates in conjunction with fish mortality rates can be helpful for identifying potential causes of
fish disorientation and entrapment within the fish passage module. This assessment could also be assisted
by examining the time delay (Table 13) that the fish passage module causes in fish migration (Katopodis
1992; OTA 1995; Larinier 2000; Schilt 2007).
Table 13. Measures of fish passage module performance
Index Status
Proportion of fish passing the module More research needed
Fish survival rate More research needed
Passage time delay More research needed
Fish injury More research needed
Proportion of fish entering fish passage entrance More research needed
Flow depth Limits available
Flow velocity Limits available
Fish passage module bed slope Limits available
Flow acceleration More research needed
Turbulent kinetic energy Limits available
Energy dissipation function Limits available
Turbulent eddy length scale More research needed
Fish passage module bed elevation change More research needed
An additional index—which is important for quantifying the performance of the fish passage module in
accomplishing the safe passage of fish—is injuries to exiting fish (Deng et al. 2005; Pracheil et al. 2016),
where a correlation between fish injury and flow acceleration patterns has been shown.
For evaluating the performance of fish attraction devices, a quantitative index is the proportion of fish
entering the fish passage module (Bunt 2001; Bunt et al. 2012; Cooke and Hinch 2013). This index can
help identify which attraction techniques, e.g., barriers, vs. behavioral attraction devices, are optimal for
the fish species encountered at the SMH facility.
Such indices aim at quantifying the performance of the fish passage module in terms of its primary
technical objective of consistently and safely passing fish through the SMH facility. As alluded to in
Appendices B.2 and B.3, however, the passage of fish through an SMH facility is intimately related to the
hydraulics of the fish passage module. For this line of thinking, additional indices quantifying the
B-17
performance of the fish passage module are also valuable (Katopodis 1992; OTA 1995). For instance, the
flow depth and velocity within the fish passage module are known to relate to the quality of fish passage.
Similarly, the bed slope of the fish passage module is known to influence the quality of fish passage
(Dermisis and Papanicolaou 2009; Noonan et al. 2012). Research has shown that the flow acceleration,
which is a surrogate of the flow patterns within the fish passage module, is related to fish injury (Deng et
al. 2005; Richmond et al. 2009). In addition, indices characterizing the turbulence levels in the fish
passage module are needed. The best-known indices for assessing the levels of turbulence are the TKE of
the flow and the EDF. However, recent work has established a relationship of the EDF to the turbulent
eddy characteristic length, which has thus gained popularity as a way of assessing the hydraulic
performance of the fish passage. The main reason for the increasing popularity of the turbulent eddy
characteristic length as a fish passage performance index is that it offers a tangible measure of the flow,
which is directly comparable to fish length, which is a species-specific attribute (Liu et al. 2006; Dermisis
and Papanicolaou 2009).
A simple but reliable measure of the fish passage module performance in terms of managing sediment is
its bed surface elevation and size fraction. Deposition of sediment, which could affect the hydraulic
performance of the fish passage module, would lead to a change in the elevation of the fish passage
module bed. In addition, monitoring of changes in the bed elevation of the bed surface topography over
time could allow estimation of the amount of incoming sediment and evaluation of countermeasures to
sediment deposition.
B.5 DESIGN CONSTRAINTS
An examination of the fish passage module requirements (Appendix B.2) and functional relationships
(Appendix B.3) allows the specification of design constraints for the fish passage module. The design
constraints can be viewed as the behaviors and features that the fish passage module must exhibit to
accomplish its primary technical objective of consistently and safely allowing the passage of fish across
the SMH facility. These behaviors and features, summarized in Table 14, are derived by mapping the
identified module requirements onto the functional relationships expressing the dominant processes that
govern the fish passage module function. At present, we do not specify strict quantitative criteria for each
of the design constraints, as the development of such criteria is beyond the scope of the present document.
Instead, identification the fish passage module performance measures outlined in Appendix B.4 provides
a basis for developing such quantitative criteria in the future. The design constraints examined in Table 14
are characterized as local when they pertain specifically to the fish passage module, and global when their
validity can be extended to the other modules of the SMH facility.
Table 14. Fish passage module design constraints
Constraint Formalization/rationale Scale (L= local,
G = global)
Module elements cannot create
barriers or drops higher than
the jumping ability of
encountered fish species
Module elements (e.g., steps, weirs) taller than the fish
jumping ability create a permanent barrier to fish movement.
Conversely, drops in elevation higher than the jumping
ability of fish may lead to fish injury or death
L
The module must create
favorable flow conditions at its
inlet for fish to enter
The flow velocity, flow depth, and turbulence levels at the
module inlet are constrained by the swimming and
orientation ability of the encountered fish species
L
The fish passage module inlet
should feature fish attraction
devices
The fish passage module should allow disoriented fish to find
its entrance
L
The fish passage module
should prevent fish from
entering the generation module
The fish passage module should prevent disoriented fish from
entering the generation module
L, G
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Table 15. Fish passage module design constraints (continued)
Constraint Formalization/rationale Scale (L= local,
G = global)
Fish passage module slope The fish passage slope is constrained by the swimming
ability of fish
L, G
Flow velocity The velocity within and at the exit of the fish passage module
is constrained by the swimming ability of the encountered
fish species
Flow depth The flow depth within and at the exit of the fish passage
module is constrained by the minimum required flow depth
for the encountered fish species
L
Fish passage module length The length of the fish passage module is constrained by the
endurance of the encountered fish species
L
Fish passage module flow
patterns
The flow patterns within and at the exit of the fish passage
module are constrained by the susceptibility of fish to injury
L
Turbulence levels in the fish
passage module
The turbulent kinetic energy, energy dissipation function, or
turbulent eddy characteristic length scale within and at the
exit of the fish passage module are constrained by the
tolerance of the fish for these quantities
L
Sediment accumulation within
fish passage module
The accumulation of sediment within the fish passage
module is constrained by the maintenance of the required
flow velocity, depth, and pattern constraints
L
Air bubble concentration
within fish passage module
The air bubble concentration in the fish passage module is
constrained by the tolerance of fish for the air bubbles
L
Module components cannot be
heavier than the lift capacity of
available cranes and transport
vehicles or vessels
The module components must not exceed the capacity of
transport vehicles or vessels and available cranes, so that they
can be transported to the SMH site and placed
G
Module components cannot
exceed in size the size of
available transport vehicles or
vessels
The module components must be smaller than the transport
vehicle or vessel to allow their transportation to the SMH site
G
Module components must be
compatible with one another
The module components must connect with one another and
offer structural stability to the module
G
Module components must be
compatible with foundation
modules
The module components must be compatible with the
foundation module to ensure the structural stability of the
module from the SMH facility foundation
G
It is also recognized herein that cost poses an additional design constraint, which plays a significant role
in the identification of optimal designs. Cost optimization, or a balancing of the costs of implementation
and operation versus the benefit of passage, must be pursued for every fish passage design to achieve
objectives, requirements, and constraints that are appropriate for a site.
B.6 DESIGN ENVELOPE SPECIFICATION
This systematic examination of the fish passage module for an SMH facility has culminated in a list of
design constraints for the fish passage module, the fulfillment of which ensures that the fish passage
module accomplishes its primary technical objective of consistently and safely passing fish across the
SMH facility. The design constraints identified in Table 14 may alternately be viewed as a design
envelope for characteristics and behaviors that successful fish passage module designs must exhibit to
ensure minimal disruption of the connectivity of the fish populations in a river by the SMH facility. Note
that multiple fish passage module designs could fulfill these design constraints, but it is not the goal of the
B-19
present report to identify the optimal design. To aid design, this report provides measures, identified in
Appendix B.4, for evaluating the performance of potential designs and identifying the optimal one.
Specification of the fish passage module design envelope requires identifying limits for the fish passage
module performance measures provided in Appendix B.4. Identification of these performance measure
limits allows excluding potential fish passage module designs with performance outside the identified
limits. For instance, a potential design for the fish passage module that allows flow velocities higher than
the darting velocity of the fish species encountered at the SMH site should not be considered. As alluded
to in Appendices B.2 and B.3, identification of such performance measure limits is subject to specific
characteristics at the SMH facility site, such as the local fish species in the example just cited. It is
possible to classify potential SMH sites with respect to some key, recurring characteristics that are
pertinent to the design envelope specification of the fish passage module. Such a classification will allow
the development of limits and designs that are applicable to a class of SMH sites with similar
characteristics, thereby enhancing SMH standardization. Site classification, which is the second pillar of
SMH, is therefore of paramount importance for identifying the limits of the fish passage module design
envelope, along with the other SMH pillars—simulation capability and testing capability.
To establish the exemplary design envelope, it is necessary to identify the pertinent spatial and temporal
scales for the fish passage module performance measures. Identifying acceptable limits for fish passage
rates for a given fish species would require identifying how far upstream and downstream from the SMH
facility, and for how long, the SMH facility effects on the populations of this fish species are evident. The
identification of these scales will also be aided by the other three pillars of SMH—site classification,
simulation capability, and testing capability.
A limitation of the current analysis is that many of the functional relationships examined in Appendix B.3
are deterministic in nature and therefore can express the processes that they model only in a deterministic
sense. The deterministic nature of these relationships implies that a given input to a process cause can
have only the specific outcome predicted by the functional relationship; for example, a given discharge in
the examined fish passage will lead to a given attraction rate of a particular fish species. Although a
design may produce certain outcomes in an average sense, the complexity and randomness in nature may
cause some variability around this predicted outcome. To account for the randomness prevalent in nature,
probabilistic relationships for the studied processes should ultimately be developed.
C-1
APPENDIX C. SEDIMENT PASSAGE MODULE
Hydropower facilities can act as barriers to the movement of sediment along a river, disrupting the
connectivity of sediment transport. This disruption has important implications for the river morphology
upstream and downstream of the hydropower facility (Schmidt and Wilcock 2008; Draut et al. 2011).
Most commonly, sediment is trapped and deposited upstream of a facility, thus reducing the water volume
and head available for power generation (Brune 1953). At the same time, entrapment of incoming
sediment upstream of the hydropower facility limits the supply of sediment downstream, thus affecting
the river morphology and planform geometry upstream and downstream of the hydropower facility, as
well as the channel stability and aquatic habitat.
There is uncertainty surrounding the need for a sediment passage module at small hydropower facilities—
sedimentation at large reservoirs has received significant attention in the literature (Kondolf et al. 2014)
although few design guidelines exist for sediment passage at small, low-head hydropower facilities. This
section will not provide the information necessary to determine whether a sediment passage module is
necessary at a site. Rather, it assumes a sediment passage module is necessary to sustain the natural
stream function of sediment transport. It is possible that sediment passage could be achieved through
other modules, such as suspended load passed over a water passage module. This multi-objective
approach is the subject of ongoing research.
C.1 OBJECTIVES
To minimize the effects caused by the disruption in the continuity of sediment transport along a river
resulting from the presence of the SMH facility, the sediment supplied from upstream must be transported
across the SMH facility (Annandale 2013; Kondolf et al. 2014; Wild et al. 2015). Thus, the transport of
sediment through the SMH facility is the primary technical objective of the sediment passage module.
To achieve the primary technical objective, the sediment passage module needs to intercept incoming
sediment from upstream while preventing its deposition upstream of the SMH facility (Figure 25).
Furthermore, the sediment passage module must maintain hydraulic conditions that allow the transport of
the supplied sediment through the SMH facility (Figure 25). The sediment routed across the SMH facility
must be transported further downstream to prevent its accumulation at the downstream end of the facility,
which might compromise the function of the other modules, such as the fish passage and the generation
module. The amount of sediment passing the SMH facility via the sediment passage module must be
sufficient to prevent degradation problems in the downstream river, such as channel incision and
overdeepening, bank erosion, and river channel migration. At the same time, the sediment transport fluxes
downstream of the hydropower facility must be such that fish habitat degradation, caused by these river
geomorphological changes or the intermittent sediment supply, is minimized. Attention must be also
given to maintaining the river water quality, which can be affected by the release and transport of finer
sediments that are typically transported in suspension (Figure 25). In summary, to achieve its primary
technical objective, the sediment passage module must accomplish a series of specific objectives:
1. Deliver incoming sediment supply to sediment passage module inlet.
2. Sustain conditions for transporting sediment across passage module.
3. Minimize sediment deposition downstream of the SMH facility.
Sediment Passage Module Primary Technical Objective
To allow the transport of incoming sediment through a SMH facility
C-2
4. Minimize river geomorphic change further upstream and downstream of SMH facility.
5. Minimize fish habitat and water quality degradation due to sediment releases.
Figure 25. Conceptual schematic of the specific objectives of a sediment passage module.
C.2 REQUIREMENTS
The requirements for the sediment passage module are quantifiable characteristics or behaviors that the
sediment passage module must exhibit to satisfy its specific objectives and thereby its primary technical
objective. The requirements for the sediment passage module are summarized in Table 16, where they are
grouped for each specific objective of the sediment passage module. This grouping highlights the
connection of the requirements with the specific objectives and thereby with the primary technical
objective of the sediment passage module. In Table 16, the module requirements are characterized as
Functional, Performance, Interface, and Other, similar to the requirements for the fish passage and other
modules (Appendix B.2). Furthermore, in Table 16 the relationship of each functional requirement for the
sediment passage module to the five constituents of the river continuum—water, sediment, energy,
organisms, and nutrients—is indicated in an analogous manner to the functional requirements for the fish
passage module (Appendix B.2).
For the sediment passage module to be able to convey sediment downstream of the SMH facility, it is
imperative that the sediment pass through the module inlet. As the flow decelerates upstream of an SMH
facility, its competence to transport sediment decreases. As a result, incoming sediment is likely to
deposit upstream of the SMH facility and not enter the sediment passage module, thereby not allowing the
sediment passage module to accomplish its primary technical objective. The resulting sediment deposition
upstream of the SMH facility, if left uncontrolled, can reduce the available head for power generation by
C-3
the generation module, thereby limiting the generation module efficiency. In extreme cases, the sediment
deposited upstream of the generation module could possibly block its intake, interrupting its operation,
and/or be entrained into the generation module intake, damaging the turbines. To minimize this risk, the
Table 16. Sediment passage module requirements. In the fourth column: F = Functional; P = Performance; I =
Interaction; O = other. In columns 6–11, an “X” denotes a relationship to the river continuum constituent indicated
in the top row
Requirement Type
(F/P/I/O) Formalization/rationale
En
ergy
Wa
ter
Org
an
ism
Sed
imen
t
Rec
rea
tion
Wa
ter
qu
ality
1
Deliver incoming sediment
supply to the sediment
passage inlet.
a
Sustain appropriate hydraulic
conditions and flow patterns
to minimize sediment
deposition and ensure
transport of sediment to the
sediment passage module
inlet
F, P, I
Upstream of the sediment
passage module, sediment
should be prevented from
depositing upstream of the
SMH facility, where
aggradation can reduce the head
used by the generation module
(GM) or clog the GM intakes
X X X X
b Use mechanical means:
walls, traps, screens F
Special barriers may be
needed to route incoming
sediment to the passage
module inlet and prevent it
from entering the GM intake
X X
2
Sustain conditions for
transporting sediment across
passage module
a Divert a sufficient portion of
the river flow F, I
A portion of the river flow
must be diverted into the
sediment passage module to
transport sediment
downstream. This portion is
thus not used by the GM or the
other modules
X X X
b
Sustain appropriate hydraulic
conditions and flow patterns
to ensure transport of
sediment through the module
F, P
The hydraulic conditions
within the sediment passage
module should correspond to
sufficient transport capacity
for the amount and sizes of
sediment encountered in the
river
X X X
3
Minimize sediment
deposition downstream of
the SMH facility
a
Sustain appropriate hydraulic
conditions and flow patterns
to ensure transport of
sediment through the module
F, P
The flow conditions and
patterns at the exit of the
sediment passage module must
have the capacity to transport
the exiting sediment amounts
and sizes further downstream
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Table 15. Sediment passage module requirements (continued)
Requirement Type
(F/P/I/O) Formalization/rationale
En
ergy
Water
Org
anism
Sed
imen
t
Recreatio
n
Water q
uality
4
Minimize river geomorphic
change further upstream and
downstream of SMH facility
a Minimize channel narrowing
and incision F, P, I
When sediment supply from
upstream is disrupted, the river
flow tends to erode sediment
from the bed, causing channel
incision
X X
b Minimize channel armoring F, P, I
When sediment supply from
upstream is disrupted, finer
sediment is gradually
winnowed away by the flow.
This leaves the coarser
immobile sediment that creates
an armoring layer on the bed,
preventing further erosion
X X
c Minimize bank erosion F, P, I
Lack of entrainable bed
sediment can lead to erosion of
bank material
X X
d Minimize changes in stream
planform geometry F, P, I
Excessive bank erosion can
lead to lateral river channel
migration and the development
of a meandering river plan
view geometry
X X
5
Minimize fish habitat and
water quality degradation
due to sediment releases
a
Sustain hydraulic conditions
to minimize settling and
intrusion of fine sediment
into the river bed substrate
F, P, I
Intrusion of suspended
sediment into the bed
interstices causes suffocation
of the fish eggs laid there
X X X
b
Sustain hydraulic conditions
to minimize suspended
sediment concentration
F, P
Excessive concentration of
suspended sediment in the
water degrades water quality
X X X X
6 Integrate structurally into
foundation module
a
Transmit all forces through
non-critical components into
the foundation module
F, P, I
The sediment passage module
will be supported instream by
a foundation module that
serves as an interface to the
streambed
X
sediment passage module must sustain appropriate flow conditions that allow incoming sediment to be
transported through its inlet. Appropriate diversion structures, such as walls, submerged vanes, or screens,
can be used to constrict and accelerate the flow, allowing the movement of the incoming sediment into the
sediment passage module. Also, because the proper operation of the generation module is a fundamental
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goal of the SMH facility, the generation module entrance must be protected by appropriate barriers
against sediment motion, such as screens, walls, or sediment traps.
A key requirement for the sediment passage module is to keep the sediment entering in motion so that it
can be transported across the SMH facility. As in the fish passage module (Appendix B.2), a portion of
the river flow must be diverted in the sediment passage module to maintain a sufficient transport capacity
to transport all sizes of incoming sediment. If this minimum transport capacity is not maintained, the
sediment will deposit within the sediment passage module (Raudkivi 1998) and, over time, the sediment
passage module may be unable to transport sediment across the SMH facility.
Because of the obstruction that the SMH facility poses to the river flow, the flow downstream of the SMH
facility is significantly decelerated and may thus lack the transport capacity required to transport exiting
sediment further downstream. As a result, the sediment exiting the sediment passage module may deposit
in its vicinity, preventing the transport of additional sediment. More important, as sediment progressively
accumulates downstream of the SMH facility, the river bed surface elevation will increase, leading to a
corresponding increase in the tailwater surface elevation. The increase in the tailwater elevation will
decrease the available head for production of energy by the generation module. The sediment passage
module is therefore required to maintain appropriate flow conditions at its exit so that sediment exiting
the sediment passage module is transported further downstream in the river.
The placement of the SMH facility disrupts the connectivity of sediment transport along the river, which
limits the supply of sediment downstream of the SMH facility (Papanicolaou 2011, p. 83). In these
downstream river reaches, the shortage of entrainable sediment from upstream causes an increase in the
transport of sediment from the river bed, which in turn causes incision of the river channel by the flow
action (Gaeuman et al. 2005; Grams et al. 2007; Magilligan et al. 2013). The channel incision can become
particularly pronounced when there is a lack of lateral sediment input to the river reaches downstream of
the SMH facility from the adjacent watershed, which intensifies the shortage of entrainable sediment
supply. The channel incision may be accompanied by channel armoring, which occurs when most of the
entrainable material has been transported downstream and only coarser material, which cannot be
entrained, remains at the river bed surface. Once river bed armoring takes place, and if the lack of
entrainable sediment supply persists, the river flow may accelerate the erosion of the banks, which is the
only remaining erodible material. Accelerated river bank erosion can lead to lateral migration of the river
channel and therefore a change in the river planform geometry with the development of river meanders.
Such changes in the river planform geometry may compromise the safety and stability of structures, such
as bridges and roads, that were adjacent to the original river channel. To prevent such significant
geomorphological changes to the river, it is necessary that the sediment passage module provide a
sufficient supply of sediment downstream of the SMH module.
C.3 INPUTS, FUNCTIONAL RELATIONSHIPS AND PROCESSES
The processes relevant to the operation and behavior of the sediment passage module are identified in the
current section, along with the functional relationships that allow quantification and prediction of these
processes. Knowledge of these processes and functional relationships is a key step for understanding the
function and predicting the behavior of the sediment passage module so that the design of the sediment
passage module minimizes the disruption of the sediment transport continuity along the river length due
to the hydropower facility. The key variables, which are the inputs to these functional relationships, are
identified first.
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C.3.1 Necessary Inputs
The key variables, which appear in the functional relationships for the sediment passage module, are
presented in Table 17. These variables are categorized in five categories, depending on their relation to
sediment, flow, geometric, and geomorphologic processes. This categorization will further allow the
systematic examination of the functional relationships to which these inputs relate.
Table 17. Key inputs for the function of the sediment passage module
Identification of
key inputs Formalization
Sediment characteristic variables
Sediment grain size distribution (e.g., median grain diameter,
geometric standard deviation), friction factor, sediment fall velocity,
sediment angularity, sediment shape, relative protrusion
Flow variables
Range of flow discharges encountered, watershed hydrologic
characteristics, flow depth, turbulent shear stress, water temperature,
friction factor
Geometric variables
Geometry and shape of passage module, elevation difference upstream
and downstream of facility, passage module slope, passage module
length, stream cross-sectional geometry upstream and downstream of
SMH facility
Geomorphologic variables River bed slope, bed topography, friction factor, channel sinuosity,
bank geometry, bank soil composition
C.3.2 Functional Relationships
The functional relationships, which express the processes that govern the transport of sediment and hence
the operation of the sediment passage module, are summarized in Table 18, along with a brief rationale
for the importance of each functional relationship.
To systematically investigate the functional relationships relevant to the operation of the sediment
passage module, it is necessary to divide the transport of sediment into two types— bedload and
suspended load (Raudkivi 1998). Bedload is the mode of transport predominantly of coarser materials—
such as coarse sand, gravel, and cobbles—which move in close proximity to the bed. In contrast, the finer
sediment—including the finer sand, silt and clay—is transported in suspension within the water column
and constitutes the suspended sediment load (Raudkivi 1998). The processes that govern the movement of
bedload and suspended load are different; therefore, the functional relationships governing their transport
are examined separately (Table 18).
Broadly, the bedload transport rate is considered a function of excess bed shear stress (Figure 26), which
expresses the difference between applied bed shear stress and critical bed shear stress for incipient motion
of the grains (Yalin 1977; Wong and Parker 2006; Parker 2008). The applied bed shear stress quantifies
the force applied by the flow that is available to set the sediment grains in motion.
C-7
Table 18. Summary of the key functional relationships relevant to operation of the sediment passage module
Relationship of To Rationale/importance
Bedload transport
rate
1. Mean flow
characteristics and
patterns
2. Turbulent flow
characteristics
3. Bed morphology
4. Critical bed shear
stress for incipient
motion
1. The main drivers of the bedload transport rate are the mean
flow characteristics, which are quantified by the bed shear stress
or stream power
2. At near-incipient conditions, turbulence may increase the
instantaneously applied shear stress to the sediment and lead to an
increase in bedload rates and bedload intermittency
3. Bedforms and/or other large roughness elements (e.g.,
boulders, large woody debris) bear a portion of the applied bed
shear stress, hence reducing the bedload rates
4. Sediment is transported as bedload as the applied bed shear
stress by the flow exceeds the critical shear stress for incipient
motion for a given sediment size
Critical bed shear
stress for incipient
motion
Sediment
characteristics
The critical shear stress for incipient motion is dependent on
sediment size, size distribution (e.g., hiding effects), and the
relative protrusion of the bed sediments
Suspended sediment
concentration
1. Mean flow
characteristics and
patterns
2. Turbulent flow
characteristics
3. Supplied
sediment
4. Settling velocity
1. The mean flow velocity is the main driver for the
transportation of suspended sediment downstream
2. Turbulence causes diffusion and mixing of the transported
sediment concentration
3. The amount of sediment transported downstream in suspension
is dependent on the amount of sediment supplied from upstream
4. The sediment settling velocity quantifies the tendency of
sediment to deposit or remain in suspension
River morphological
change
1. Bedload and
suspended sediment
transport capacity
2. Bank properties
1. The transport capacity of a river determines the amount of
sediment that the river can transport for a given set of flow and
sediment conditions. Imbalances between sediment transport
capacity and supply result in aggradation or degradation of the
river
2. The type of material and geometry of the river banks determine
how prone the river is to lateral migration and change in its
planform geometry
The applied bed shear stress is considered to be a function of the flow depth, the slope of the sediment
passage module bed, and the density and the size of the sediment grains to be transported. Because the
bed shear stress is a function of the flow depth, it follows that indirectly it is dependent on the variables
that influence the flow depth in a river. As a result, the bed shear stress is also dependent on the flow
discharge and the resistance exhibited by the river bed surface to the flowing water. As is presented in
detail in Appendix E of this report, resistance to the river flow is, in turn, related to the size distribution of
the sediment grains making up the river bed. Overall, resistance to flow, and hence the friction factor,
which is a quantitative measure of resistance, increases with larger bed grain sizes. The friction factor is
also a function of the relative submergence—the ratio of the flow depth to the characteristic height of the
sediment making up the bed. In rivers with large roughness elements, such as large boulders, bedforms,
and logs, it is possible for the flow depth to be less than the sizes of these elements. Under such
conditions, the friction factor becomes an inverse function of the relative submergence, i.e., the ratio of
the flow depth and the roughness element size (Millar 1999; Ferguson 2007; Rickenmann and
Recking 2011).
C-8
Figure 26. Correlation of the bedload transport rate (vertical axis) with the excess
bed shear stress (horizontal axis). The critical bed shear stress is considered equal
to 0.047. (Wong and Parker 2006; With permission from ASCE)
The critical bed shear stress for incipient motion is the minimum amount of force applied by the flow that
is required to set a grain with a given size in motion. The critical bed shear stress for incipient motion is
broadly dependent on the size and heterogeneity of the bed material grains, their packing density, their
shape, and their degree of protrusion into the flow (Yalin 1977; Wiberg and Smith 1987; Papanicolaou et
al. 2002). Clearly, larger grains are heavier and require more force applied by the flow to be entrained. At
the same time, the heterogeneity of the bed material plays an important role in the critical bed shear stress
for incipient motion. Specifically, when both larger and smaller grains are present atop the river bed, the
larger and thus more stable grains hide the smaller grains from the flow action, thereby reducing the
likelihood that smaller grains will be entrained (Parker 2008; Kleinhans and van Rijn 2002). Similarly,
when the packing density of the entrainable sediment increases, it is more unlikely that sediment grains
will be dislodged and transported by the flow. The shapes of sediment particles also influence their
critical stress for incipient motion. More elongated grains are more stable and tend to be harder for the
flow to entrain, compared with more round grains. Also, sediment grains, which are more angular, tend to
interlock more strongly with the bed substrate grains and therefore require more force from the flow to be
entrained. The sediment grain protrusion also plays an influential role on the entrainment of the grains. As
the degree of grain protrusion decreases, the area of the grain exposed to the flow action decreases, and
thus a higher force is required to entrain the grain (Figure 27) (Wiberg and Smith 1987).
Finer sediment is typically transported in suspension (Raudkivi 1998). The suspended sediment is
considered to settle out of suspension and deposit when a characteristic velocity length scale of the flow
called “friction velocity” is less than the settling velocity of the suspended sediment (Figure 28). The flow
shear velocity is a surrogate measure of the bed shear stress and depends on the flow depth and bed slope,
while the fall velocity is determined from the sediment size and water temperature (Raudkivi 1998).
C-9
Figure 27. Critical shear stress as a function of the grain Reynolds number for different degrees of grain
protrusion, denoted as (p/D), in relation to the flow and different grain shapes. (After Moore 1994 in
Papanicolaou and Abban et al. 2016)
Figure 28. Percentage of sediment transported as bed load and suspended load as a function
of the ratio of sediment fall velocity to friction velocity. (After Papanicolaou and Abban 2016)
The amount of suspended sediment being transported by the flow is known as the “suspended load flux.”
It is the product of the flow velocity and the suspended sediment concentration (Figure 29). As discussed
in detail in Appendix E of this report, the flow velocity in the river or within the sediment passage module
depends on the flow discharge, the cross-sectional geometry, the bed resistance, and the bed slope. The
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suspended sediment concentration expresses the amount of sediment in suspension in the water column,
which may come from three sources: (1) sediment yield from the watershed, (2) erosion and uplift from
the river bed, and (3) erosion from the river banks. These three sources are examined separately in the
following paragraphs.
Figure 29. Relationship of suspended sediment load (vertical axis) to the flow discharge and
watershed steepness (horizontal axis). (van Rijn 1993)
The supply of sediment from a watershed to its rivers is a complex phenomenon that has been studied
extensively (Milliman and Farnsworth 2013; Abban et al. 2016). In short, the yield of suspended sediment
from the watershed to a river depends on the watershed drainage area; the precipitation and water runoff;
the watershed topographic characteristics, such as shape, size, slope and elevation; the watershed soil
type; and the types of land use and land cover in the watershed. The erosion and uplift of finer sediment
from the river bed into suspension is a function of the prevailing flow conditions in the river and the
sediment size. As indicated in Figure 28, when the friction velocity is significantly smaller than the
sediment fall velocity, then sediment tends to become suspended. The contribution of material from the
erosion of the river banks is an outcome of the imbalance between the flow force acting on the river banks
and the resistance to erosion offered by the bank material (Langendoen and Alonso 2008; Langendoen
and Simon 2008; Sutarto et al. 2014). The flow force is quantified by the shear stress acting on the river
bank, and the bank material resistance to erosion is quantified by the material erodibility and critical shear
strength. These two parameters depend on the physical properties of the bank material soil (e.g., sediment
type and size distribution, bulk density), along with a suite of geochemical properties (e.g., soil clay type,
water chemistry) and biological properties (e.g., vegetation cover, burrowing animals). (Grabowski et al.
2011) Note that the contribution of bank material to the river may also be caused by bank mass failure, in
which large sections of the bank lose their stability, fall into the river, and are eroded by the flow action
(Langendoen and Alonso 2008; Sutarto et al. 2014).
Geomorphic change in a river reach is an outcome of the imbalance between the transport capacity of a
river and the sediment supply to its reach from its upstream reaches. It can be shown that this imbalance is
an outcome of variations in the sediment transport rate along the river, which result in changes in the river
topography over time (Parker 1991; Viparelli et al. 2010).
C-11
C.4 MEASURES OF MODULE PERFORMANCE
Assessing the efficiency of the sediment passage module in meeting the requirements listed in
Appendix C.2 requires quantifiable indices (Table 19). Such indices will in turn allow evaluation of the
degree to which various designs for the sediment passage module accomplish its specific and primary
technical objectives and evaluation of the optimal design.
Table 19. Sediment passage module measures of performance
Index Status
Indices of Schmidt and Wilcock (2008) Limits available—modeling needed
Indices of Grant et al. (2003) Limits available—modeling needed
River width Limits available
River topography Limits available
Bedload transport rate Limits available
Bed slope Limits available
Grain size distribution Limits available
River planform geometry Limits available
Suspended sediment flux Limits available
The assessment of sediment passage module performance, with respect to maintaining sufficient sediment
transport capacity in the river reaches downstream of the SMH facility, needs to involve measures
quantifying the river geomorphic change. Such measures are the three complementary indices proposed
by Schmidt and Wilcock (2008), which quantify (1) the potential for river aggradation or degradation, (2)
the bed incision potential, and (3) the magnitude of flood reduction under the conditions before and after
the installation of the SMH facility. Starting from a conceptual relationship for river morphological
stability proposed by Lane (1955), Schmidt and Wilcock (2008) derive an index for the potential for river
aggradation and degradation, which considers the river discharge, sediment transport rate, and
representative grain size in a river reach before and after the placement of the SMH facility. Because
aggradation or degradation is a necessary but not sufficient condition for river incision, an index for the
river bed incision potential is also proposed. The bed incision potential index for a river reach is based on
a formulation similar to the bed shear stress. It is a function of the flow depth after the SMH facility
placement, the river bed slope upstream of the hydropower facility installation, and the characteristic
grain size at the time of the hydropower facility installation. To account for the reduction in competent
flows for sediment transport following the placement of a hydropower facility, the third index of Schmidt
and Wilcock (2008) considers the ratio of 2 year floods before and after the placement of the hydropower
facility. Following a systematic analysis of these indices, in conjunction with observed geomorphic
changes in rivers downstream of existing hydropower facilities, Schmidt and Wilcock (2008) provide
ranges for the indices, which correspond to minimal changes in river geomorphology (Figure 30 and
Figure 31).
In an earlier work, Grant et al. (2003) proposed a set of two indices, different from those of Schmidt and
Wilcock (2008), for assessing the geomorphologic effects of dams. Specifically, Grant et al. (2003)
consider (1) the ratio of the sediment supply upstream and downstream of the SMH facility and (2) the
ratio of the fractions of sediment-transporting flows before and after the placement of the SMH facility. In
river reaches where sediment supply is considerable lower than the transport capacity, morphologic
changes such as bed erosion, incision, narrowing and armoring are expected to take place (Grant et al.
2003; Magilligan et al. 2013). This regime corresponds to the lower right area of the plot of Figure 32. In
the opposite case, river reaches with limited sediment transport capacity but high sediment supply— for
instance, due to lateral watershed contributions—tend to aggrade. The river morphology will experience
subtle effects in reaches where sediment transport capacity and supply are nearly in balance,
corresponding to the center of the graph in Figure 32.
C-12
Figure 30. Threshold values of (a) the index for sediment aggradation and degradation and (b) the index of
incision potential for various hydropower facilities. (Schmidt and Wilcock 2008)
Figure 31. Threshold values of (a) the index for flood magnitude reduction and (b) the index of incision
potential for various hydropower facilities. (Schmidt and Wilcock 2008)
C-13
Figure 32. Thresholds of the morphologic change indices of Grant et al. (2003) where the effects of
hydropower facilities on river morphology are subtle.
To fully assess the effects of an SMH facility on the downstream river morphology, a systematic survey
of the river topography, width, bed slope, and planform geometry is necessary. Furthermore, monitoring
the grain size distribution would allow assessment of whether armoring is taking place. In addition,
assessing the efficiency of the sediment passage module in conveying sediment through the SMH facility
requires monitoring of the bedload transport rate and the suspended sediment flux. At the same time,
monitoring the river bed topography upstream and downstream of the SMH facility allows the evaluation
of potential sediment deposition around the SMH facility.
C.5 MODULE DESIGN CONSTRAINTS
As is the case for the fish passage module, the design constraints (Table 20) for the sediment passage
module are derived by mapping the sediment passage module requirements (Appendix C.2), onto the
functional relationships (Appendix C.3). The design constraints can be viewed as the behaviors and
features that the sediment passage module must exhibit to accomplish its primary technical objective of
allowing the transport of sediment across the SMH facility. We do not specify strict quantitative criteria
for each of the design constrains, as the development of such criteria is beyond the scope of the present
document. Instead, the identification of the sediment passage module performance measures outlined in
Appendix C.4 provides a basis for developing such quantitative criteria in the future. For the other
modules, the design constraints examined in Table 20 are characterized as local when they pertain
specifically to the sediment passage module and global when their validity can be extended to the other
modules of the SMH facility.
C-14
Table 20. Sediment passage module design constraints
Constraint Formalization/rationale Scale (L= local,
G = global)
The sediment passage module
must create favorable flow
conditions at its inlet for
sediment to enter
Sediment that does not enter the sediment passage module
will likely deposit upstream of the SMH facility, causing
loss of available head for power generation and
interference with the operation of the other modules
L
The sediment passage module
inlet must prevent incoming
sediment from being
entrained into the generation
module (GM) and from
clogging the GM inlet
Sediment entrained into the turbines will cause damages to
the turbines. Also, clogging of the GM intake will reduce
the turbine efficiency and energy production
L
The bed shear stress within
the sediment passage module
must exceed the critical bed
shear stress for incipient
motion of all encountered
sediment sizes
Sediment with critical bed shear stress for incipient motion
higher than the applied bed shear stress will deposit within
the sediment passage module, preventing it from
accomplishing its primary technical objective
L
The sediment passage module
must supply sufficient
amounts and sizes of
sediment downstream to
minimize channel
morphologic change
Failure to supply sufficient amounts and/or sizes of
sediment downstream of the SMH facility will lead to
often undesired river morphologic changes, such as
incision, armoring, and lateral migration
L
The sediment passage module
geometry should be sufficient
for handling all sizes and
amounts of sediment
encountered by the river
If the geometry of the sediment passage module—i.e.,
width, opening size— is not adequate for the size and
amounts of sediment required to be transported, sediment
will accumulate upstream and within the module,
preventing its transport downstream
L
The bed shear stress at the
exit of the sediment passage
module must exceed the
critical bed shear stress for
incipient motion of all
encountered sediment sizes
If the shear stress applied by the flow is smaller than the
critical shear of the transported sediment, sediment will
deposit downstream of the SMH facility, decreasing the
available head for power generation, impairing the
function of the adjacent modules, and limiting the supply
downstream
L, G
Module components need to
be able to withstand the
impact of the largest sediment
expected
Impacts from incoming sediment could lead to damage to
the structure of the module, which must be minimized
G
Module components cannot
be heavier than the lift
capacity of available cranes
and transport vehicles or
vessels
The module components must not exceed the capacity of
transport vehicles or vessels and available cranes, so that
they can be transported to the SMH site and placed
G
Module components cannot
exceed in size the size of
available transport vehicles or
vessels
The module components must be smaller than the
transport vehicle or vessel to allow their transportation to
the SMH site
G
Module components must be
compatible with one another
The module components must connect with one another
and offer structural stability to the module
G
Module components must be
compatible with foundation
modules
The module components must be compatible with the
foundation module to ensure the structural stability of the
module from the SMH facility foundation
G
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C.6 DESIGN ENVELOPE SPECIFICATION
This section of the report derives a list of design constraints for the sediment passage module, which are
intended to guide design so that the sediment passage module will best accomplish its primary technical
objective of transporting sediment across the SMH facility. Multiple sediment passage module designs
could fulfill these design constraints, but the present report does not aim to identify the optimal design.
Rather, we provide in Appendix C.4 a set of indices that can be used to assess the optimal design for the
sediment passage module.
Specifying the design envelope for the sediment passage module requires establishing limits for the
performance measures outlined in Appendix C.4. Identifying these performance measure limits allows the
exclusion of potential sediment passage module designs that do not perform within the identified limits.
For instance, a water passage module design allowing incoming sediment accumulation at the generation
module intake cannot be considered. The identification of these limits is influenced by specific
characteristics of the SMH facility site, including the hydrologic regime of the watershed where the SMH
facility site is located, as well as the grain size distribution of the sediment transported along the river. It
is possible to classify potential SMH sites with respect to these key, recurring characteristics that are
pertinent to the design envelope specification of the sediment passage module. The outcome of such
classification schemes will be to establish limits and designs that apply to a class of SMH sites with
similar characteristics, thereby enhancing SMH standardization. For the other modules, site classification,
the second pillar of SMH, is of paramount importance for identifying the performance limits for the
sediment passage module design envelope, along with the other SMH pillars, simulation capability and
testing capability.
The concept of scale is particularly important for the sediment passage module, as the sediment
transported by the sediment passage module across the SMH facility and conveyed further downstream
may significantly impact the morphologies of river reaches far downstream of the SMH facility. For
instance, Schmidt and Wilcock (2008), in the case of larger dams, considered river reaches as far as 180
miles downstream to test their proposed indices of geomorphic change. It is necessary, therefore, to
delineate the spatial and the temporal scales at which the SMH facility affects sediment supply. Of
paramount importance in identifying the spatiotemporal scale are the testing capability and especially the
simulation capability of the SMH concept, which can be used to simulate potential effects of the SMH
facility in the river continuum.
A limitation of the current analysis is that all of the functional relationships examined in Appendix C.3
are deterministic in nature. The deterministic nature of these relationships implies that a given input to a
process cause can have only a specific outcome, which is predicted by the functional relationship.
However, complexities such as river turbulence and river bed surface irregularity often cause variability
in the outcome of processes, which are not predicted by deterministic relationships. In the future,
additional research should focus on replacing the currently used deterministic relations, such as those
included in Appendix C.3, with their probabilistically based counterparts.
D-1
APPENDIX D. RECREATION PASSAGE MODULE
By disrupting the flow of water, hydropower facilities can have significant impacts on recreation, a key
activity and economic resource in many rivers (Bonnet et al. 2015). Recreational craft have three options
for traversing a hydropower facility: exit the water and portage the craft around the dam, use a lock
structure that mechanically raises the water level or lifts a boat from the downstream water surface
elevation to the upstream water surface elevation (or vice versa), or use a passive canoe or boat chute that
carries small craft through a channel-type structure built into or around the facility. When none of these
three options is readily available, a boat or paddler must reverse course.
The economic and social impacts of hydropower facilities on recreation are apparent—the most common
Federal Energy Regulatory Commission–mandated mitigation measure at small hydropower plants
undergoing relicensing is “the preparation and implementation of plans to monitor or study recreational
site usage or plan for the implementation of recreational sites and improvements” (Bevelhimer et al.
2015). A recreation passage module integrated into the facility in the design phase has the potential to
create new recreation opportunities and serve as a local asset.10
At large hydropower facilities on navigable inland waterways, locks that pass commercial traffic are
sometimes available for use by recreational watercraft. It is not anticipated that these types of structures
meet the ecological compatibility, cost-optimized, modular approach that SMH facilities will embody,
and they are not considered in this section. At small, low-head dams, passage structures for small canoes,
kayaks, and whitewater rafts have been implemented over the past few decades (Caisley et al. 1999;
Bombardelli et al. 2002; Colorado Water Conservation Board 2008). Caisley et al. (1999) note that few
design guidelines for canoe chutes are documented, and new designs have generally required a physical
model study accompanied by computational models to fully understand the chute hydrodynamics.
Furthermore, hydropower facilities could create hazardous flows, such as large eddies, sudden drops of
the water surface, large surface waves, high velocities, and hydraulic jumps, that would endanger
recreational craft, especially smaller craft such as canoes and kayaks. The presence of a recirculating
hydraulic jump is of particular concern, as that condition has been known to cause fatalities throughout
the United States.11
D.1 OBJECTIVES
To mitigate the adverse consequences of hydropower facilities on river-based recreation, provision needs
to be made for a recreation passage module. The primary objective of the recreation passage module is to
allow the passage of small recreational craft consistently and safely through the hydropower facility.
To accomplish its primary technical objective, a recreation passage module needs to accomplish the
following specific objectives (Figure 33):
1. Operate within a known range of recreation performance difficulty.
2. Provide a safe and visible entrance for recreational craft into the module.
10
See for example http://www.denverpost.com/2007/07/14/the-south-platte-a-rivers-rebirth/ 11
http://krcproject.groups.et.byu.net/browse.php
Recreation Passage Module Primary Technical Objective
Allow the passage of small recreational craft consistently and safely through a SMH facility
D-2
3. Allow recreational craft to safely cross the hydropower facility.
4. Allow recreational craft to exit safely into the river downstream of the module.
5. Provide for emergency rescue personnel and apparatus.
6. Integrate structurally into foundation module.
Figure 33. Conceptual schematic of the specific objectives of a recreation passage module.
It is noted that hydropower facilities could indirectly affect recreation outside their immediate vicinity.
The reduction of flows downstream of hydropower facilities could make river reaches unnavigable by
many types of vessels used for recreation purposes, such as boating, whitewater rafting, and fishing,
thereby eliminating these activities. In addition, changes in the river geomorphology downstream of a
hydropower facility—such as river bed aggradation, lateral migration, and narrowing—could impact
near-stream activities, including camping, hiking, and aesthetic enjoyment. Finally, degradation of fish
habitat and fish populations downstream of hydropower facilities could have significant consequences on
recreational fishing. However, these indirect effects can be mitigated by the operation of the water,
sediment, and fish passage modules, as covered in detail in Appendices E, C, and B, respectively, of the
present document. Therefore, the indirect effects of the hydropower facility on recreation are not
considered in this section.
Recreational craft may wish to travel upstream through a hydropower facility. While this is an important
connectivity issue to address, contrary to upstream fish passage, recreational craft cannot be conveyed
upstream without heavy mechanical equipment (i.e., a lock, lift, or onshore mechanical track). Future
recreation passage modules may include this functionality, but for simplicity, cost optimization, and
alignment with modern day canoe and kayak courses, the recreation passage module exemplary design
only accommodates downstream movement.
D-3
D.2 REQUIREMENTS
The requirements of a recreation passage module are derived to ensure the safety of passengers while
balancing length and cost (Table 21). General requirements are referenced from Klumpp et al. (1989),
Caisley et al. (1999), and Colorado Water Conservation Board (2008).
Table 21. Recreation passage module requirements. In the fourth column: F = Functional; P = Performance; I =
Interaction; O = other. In columns 6–11, an “X” denotes a relationship to the river continuum constituent indicated
in the top row
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter Q
ua
lity
1 Determine the desired degree
of passage difficulty F
A passage module may be designed
for canoes or for inexperienced
boaters who require shallow
gradients and low drops. The
module may also be designed to
create difficult-class rapids if
located in a whitewater region. This
decision will dictate hydraulic
requirements
X X X
2
Provide a safe and visible
entrance for recreational craft
into the module
F, I
The module entrance must be
clearly marked with signage that is
visible from the stream to ensure
that boaters unaware of the passage
module are alerted to its presence.
X
a Exhibit consistent and smooth
approach hydraulics F, P, I
The module should attract boaters
while ensuring their safety under a
range of flow conditions. The
upstream headwater elevation
should remain nearly constant,
meaning an entry gate or transition
zone must pass variable-flow rates
X X
b
Provide for audible or visual
warning signs identifying the
passage entrance
F
The passage entrance must be
clearly visible to those traveling
downstream who may be unaware
of the module
X
c Control inflow to acceptable
levels F, P, I
The entrance to the module will act
as a control device for flows
through the module. It will not be
desirable to pass flood flows
through the module, as they may
result in scouring within the module
and will create dangerous hydraulic
conditions for anyone attempting to
pass. It will be desirable to maintain
a consistent inflow rate over a wide
range of flows, which can be
achieved through an active or
passive regulation system
X X
D-4
Table 20. Recreation passage module requirements (continued)
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter Q
ua
lity
3
Allow recreational craft to
safely cross the hydropower
facility
F X X X
a Exhibit consistent and smooth
passage hydraulics F, P
The recreation passage module
should be safe under all flow
conditions, with the module
smoothly and continuously sloping
downstream, and eddies should
have low velocities so a swimmer
can escape from them. Many boat
chutes include a notched “V” down
the center of the flow path to both
guide boats through the center of the
channel and ensure flow is
concentrated under low-flow
conditions
X X
b Optimize module width F, P
The module should be wide enough
to accommodate recreational craft
while allowing someone to easily
maneuver around the craft. Sloping
walls are preferred to vertical walls,
as they mitigate the effects of
surging and reflected waves
(Simmons et al. 1977)
X X X
c Optimize water velocity and
depth through the module F, P
Velocity and depth of water flow
through the module are closely
related. A high velocity will result
in shallow water, sloshing, and large
eddies. Depth should be sufficient to
immerse the hull of the craft and
allow paddles to be effectively
submerged
X X X
d Provide natural in-module
features F
The inclusion of boulders, smooth
natural rocks, or artificial rocks
should be considered. Artificial
obstacles with simple and smooth
shapes are preferred to enable
precast fabrication or the use of
forms that can be reused at multiple
modules
X X X
4
Allow recreational craft to
exit safely into the river
downstream of the module
F, P, I X X X
a Exhibit consistent and smooth
exit hydraulics F, P, I
The downstream module exit into
the channel is the location where a
recirculating hydraulic jump or
“keeper” roller can form. This
X X X
D-5
Table 20. Recreation passage module requirements (continued)
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter Q
ua
lity
condition must be mitigated under a
wide range of flow conditions
b Provide for a recovery pool F, I
Many boat chutes include a
recovery pool to allow the paddler
to perform an Eskimo roll to right a
capsized vessel
X X X
5 Provide for emergency rescue
personnel and apparatus F
Warning signs and audible warning
systems, buoys, and physical
separation between the recreation
passage module and generation
modules should be incorporated into
module design. The module design
must consider appropriate access for
emergency personnel, which may
include anchor points within the
module or on the module periphery
X
6 Integrate structurally into
foundation module
a
Transmit all forces through
non-critical components into
the foundation module
F, P, I
The recreation passage module will
be supported instream by a
foundation module that serves as an
interface to the streambed
X
D.3 INPUTS, FUNCTIONAL RELATIONSHIPS AND PROCESSES
D.3.1 Necessary Inputs
The variables necessary to quantify recreation passage module functional relationships are presented in
Table 22. These can be categorized as relating to either the physical features and flow characteristics of
the site, or the type of watercraft and passage experience to be designed for. This categorization will
further allow the systematic examination of the functional relationships to which these inputs relate.
Table 22. Recreation passage module necessary inputs for hydraulic design
Identification of
key inputs Formalization
Flow characteristics
Range of discharge available under normal conditions, inflow Froude
number, stage-discharge relationships for headwater and tailwater at an
SMH-type facility
Head Headwater and tailwater elevations under normal conditions, depth
Site characteristics
Stream width, presence of boulders or other sharp or dangerous submerged
structures, presence of eddies, design head of SMH facility, streambed
elevation, bed slope
D-6
Table 21. Recreation passage module necessary inputs for hydraulic design (continued)
Identification of
key inputs Formalization
Recreation vessel type Type (canoe, kayak, raft), size, shape, weight, depth
Degree of difficulty Identification of the intended use—whether kayak, canoe, or whitewater
raft—as this will determine the design hydraulics
Characteristics of person on vessel Weight, age, experience
D.3.2 Functional Relationships
The functional relationships important to the design of a recreation passage module are summarized in
Table 23, along with a brief rationale for the importance of each functional relationship.
Table 23. Summary of key functional relationships necessary for recreation passage module design
Relationship of To Rationale/importance
Module size, shape,
number of drops,
slope, and discharge
Type of hydraulic
jump
A hydraulic jump occurs when high-velocity flow transitions to
low-velocity flow. These conditions will be present at abrupt
drops within the module and at the point of discharge from the
module into the tailwater. Hydraulic jumps that maintain a
positive downstream velocity at all times are desirable, whereas
those that create recirculating rollers are not
Range of discharges
1. Water velocity
through module
2. Water depth
through module
3. Regulation of water
velocity and depth
The relationship between discharge and depth/velocity through
the module should be known to ensure the module is passable
under most flow conditions. If safe passage cannot be
guaranteed, mechanical regulation of the inflow may be
necessary, although this may not prove economically feasible.
Gross head at site
Minimum module
length, gradient, and
flow
Recreational craft require a safe gradient to bridge the abrupt
drop required for hydroelectric generation. This is accomplished
through a single downstream sloping module or through a series
of drops. A relationship predicting the length and gradient
associated with each type based on the gross head at a site is
necessary. The range of flow rates that can be sustained through
the module based on this gradient must be considered
Size, velocity, and
location of eddies
around and in the
module
Travel path of
recreational craft
Eddies dissipate turbulent kinetic energy, resulting in
recirculation and swirling flows that could trap a small
watercraft or a capsized paddler.
Module exit
hydraulics
1. Changes in
downstream flow
depth
2. Scour
A downstream depth that rises and falls during periods of
variable discharge will have an effect on the hydraulics of the
module exit, an area that is vulnerable to recirculating flow
patterns. The flow exiting the module may also result in some
scour downstream. This relationship should be understood and
scour minimized
All recreation passage downstream of an SMH facility will require a hydraulic drop to connect a craft
from the headwater to the tailwater. This is generally achieved using either boulders or a series of drops
(Caisley and Garcia 1999). In the case of boulders, there is large uncertainty in maintaining and
controlling a safe flow under a variety of conditions, owing to the roughness of the boulder surfaces and
the presence of holes between boulders, which create highly unsteady flow. When drops are used, they
must be carried out in series, with sufficient length between them to ensure there is no interference from
D-7
the backwater profile extending upstream from the next drop. Determining this length requires a physical
model study or simulation. An appropriate depth of drop is based on two conditions: it must be shallow
enough that large waves do not submerge the front of the craft (if designing for a canoe), and it must be
sized to avoid the creation of a recirculating hydraulic jump.
The behavior of a hydraulic jump at an abrupt drop is a widely studied phenomenon, as summarized in
Caisley and Garcia (1999). The complex hydrodynamics are a function of discharge, hydraulic head,
water depth, and the geometry of the channel. As proposed by Hsu (1950), a hydraulic jump can be
classified into five regions based on the approach flow Froude number and the depth downstream of the
abrupt drop (Figure 34). The jump begins to travel upstream in Region 1, when the toe of the jump is
upstream of the drop. This region also produces the highest tailwater elevation. In Region 5, the toe
travels downstream past the drop, and the tailwater elevation is at a minimum. At regions 2 and 4, the
jump is stable and the drop controls the location of the jump. In these regions, breaking, recirculating
surface waves are created. In Region 3, undulating waves (i.e., waves that do not break) travel
downstream and there is no zone of recirculation. Based on guidelines developed by Taggart et al. (1984),
a boat chute design should ensure a jump remains in Region 3, or the lower or upper portion of Region 2
or Region 4, respectively. These regions will carry boaters downstream while minimizing the risk of a
roller that can trap them underwater.
Figure 34. Hydraulic jump behavior at an abrupt drop. (Caisley et al. 1999 as adopted from Hsu et al. 1950)
The hydraulic jump is also classified as an A-jump, a B-jump, or a wave jump, loosely corresponding to
Regions 1 and 2, Regions 4 and 5, and Region 3, respectively. A prediction of the type of jump to be
formed at an abrupt drop is provided by Moore and Morgan (1959), who base their estimate on a Froude
number (V1/(gY1)0.5
), the ratio of downstream to upstream water depth (value of y2/y1), and the ratio of the
depth of drop to the upstream water depth (Zo/ y1), where the subscripts 1 and 2 refer to upstream and
downstream of the toe of the jump, respectively. It is seen that a finite band of values exists for a range of
potential Froude numbers where the desirable wave jump occurs (Figure 35). It is possible to design a
variety of passage module shapes and sizes that will create favorable conditions for watercraft. However,
these equations, among others that describe the hydraulic jump, have been derived using controlled
hydrodynamic conditions in a flume; and in practice, the predicted outcomes may not match the results of
physical model studies (Taggart et al. 1984). Computational and physical models provide valuable
insights into hydraulic conditions under a variety of discharges that will be necessary for module design.
D-8
Figure 35. Prediction of hydraulic jump type. (Caisley and Garcia 1999 as found in Moore and Morgan 1959)
The presence of a hydraulic jump can also be mitigated with an inlet control structure that modulates the
inflow discharge and velocity. Some boat chutes employ a hinged flap gate to regulate the flow through or
into the passage channel (Figure 36). The flap is lifted and lowered based on upstream conditions,
creating a change in velocity and water surface elevation. A particularly effective design incorporates a
slotted apron as the downstream flap of the hinge, allowing water to pass under the crest of the hinge and
resurface downstream (Caisley and Garcia 1999). This configuration helps create an undulating hydraulic
jump with surface waves that travel continuously downstream. However, mechanical regulation adds cost
and complexity to the design, which may compromise the overall feasibility of the module. The need for
and method of flow control at the entrance of the module must be well understood and optimized for cost
and efficiency of use over a wide operating range.
D-9
Figure 36. Inlet control structure designed with a slotted apron that creates an undular
hydraulic jump with no recirculation. (Caisley and Garcia 1999)
A relationship between module length, gradient, head, and in-module flow at a site is critical to assessing
the feasibility of a module design. This relationship will depend strongly on type of passage (e.g., sloping
channel or abrupt drops), degree of difficulty desired, and site geometry. On a site scale, Simmons et al.
(1977) offer a classification of whitewater difficulty for a range of channel slope and flow (Figure 37). It
is seen that as flow increases at a given slope, the difficulty and class of rapids is also increased. Similar
relationships are necessary for module designs to predict the navigation of a module or series of modules
under various flows.
Figure 37. Whitewater classification versus slope and flow. (Simmons et al. 1977)
D-10
D.4 MEASURES OF PERFORMANCE
The recreation passage module is intended to provide safe and consistent passage to small craft that wish
to cross the hydropower facility. A variety of module types can accomplish this objective, and evaluation
criteria are needed to quantify the difficulty of the module, the operational range of the regulating
technology, flow velocity and depth, size, and cost (Table 24).
Table 24. Recreation passage module measures of performance
Index Status
Difficulty of module Limits available—more research needed
Hydraulic jump Limits available—modeling needed
Viable range of flow More research needed
Acceptable slope More research needed
Cost of operation More research needed
The passage difficulty of the module should be clearly understood and communicated to paddlers,
canoeists, and kayakers. In the United Kingdom, boat chutes on the Medway River are classified using a
1 to 3 rating system12
based on the slope of the chute. A more quantitative recreation performance index
can be used to evaluate the potential for destination whitewater or boating recreation (Colorado Water
Conservation Board 2008):
𝑅𝑒𝑐𝑟𝑒𝑎𝑡𝑖𝑜𝑛 𝑃𝑒𝑟𝑓𝑜𝑟𝑚𝑎𝑛𝑐𝑒 𝐼𝑛𝑑𝑒𝑥 = 𝐻𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝐷𝑟𝑜𝑝
𝐶𝑜𝑢𝑟𝑠𝑒 𝐿𝑒𝑛𝑔𝑡ℎ∗ 𝐷𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 ∗ 100 (D.1)
A minimum performance index of 75 is the target for a “reasonable recreational experience” at a
destination boating area, and a value of 500 reflects world-class whitewater or kayaking potential. While
a similar approach could be applied to recreation passage modules, more research is necessary to classify
module types and recreation opportunities.
Module performance with respect to the creation of a hydraulic jump is highly dependent on geometry
and flow characteristics. For drop structures, Caisley et al. (1999) offer empirical predictions of hydraulic
jump types based on the results of model studies (Figure 38). A clear dividing line between jump types is
shown as the difference between tailwater depth, hd, and the downstream height of the step, ha, increases.
This measure is applicable for a single type of structure; and more research, including physical testing, is
necessary to fully categorize this behavior for different recreation passage module types.
12
http://www.rivermedwaycanoes.com/guid-to-canoe-passes-and-locks/
D-11
Figure 38. Empirical prediction of hydraulic jump type. (Caisley et al. 1999)
A measure of acceptable flow velocity and depth is required for different types of passage. Criteria can be
developed similar to those of Hyra (1978), who provides optimum, acceptable, marginal, and
unacceptable ranges of depth and velocity for different types of recreation based on safety minimum and
maximum criteria and probabilities of use (Figure 39).
Figure 39. Suggested depth and velocity criteria for canoeing and kayaking. (Hyra 1978)
D-12
D.5 DESIGN CONSTRAINTS
The analysis of the recreation passage module requirements (Appendix D.2) in conjunction with the
functional relationships (Appendix D.3) allows the specification of design constraints for the recreation
passage module (Table 25). These are considered the behaviors and features that the recreation passage
module must exhibit to accomplish its primary technical objective of allowing small watercraft to pass
consistently and safely through the SMH facility. The design constraints are not prescribed for a specific
site or module type, but rather form a framework from which specific designs can be created and
quantitative evaluation criteria developed. Design constraints are characterized as local when they pertain
specifically to the recreation passage module and global when their validity can be extended to the other
modules of the SMH facility.
Table 25. Recreation passage module design constraints
Constraint Formalization
Scale
(L= Local,
G = Global)
Avoid creating a recirculating hydraulic
jump under normal conditions
Safety is the primary consideration of the
recreation module, and the threat of a
recirculating hydraulic jump is the most
significant design challenge for passing small
craft. A basic design constraint is outlined in
Taggart et al. (1984): “any supercritical flow
must make the transition to subcritical flow
with the supercritical discharge on the
surface and on a horizontal attitude.” A flow
control device at the module entrance may be
necessary if it cannot be ensured that a
hydraulic jump is prevented under a wide
range of flows.
G, L
Mitigate all personal safety risks within
the module
The risk of injury, drowning, or death is
present at all hydraulic structures intended
for use by recreationists. Recreation passage
module personal safety risks that must be
mitigated include but are not limited to sharp
edges or protrusions, holes or objects that
entrap arms or legs, pinning against objects
or walls, lack of an appropriate flow path
downstream, and entrapment into the
generation module region
L
Limit the maximum hydraulic drop of
individual drops within the module
The recreation passage module may
incorporate a series of small drops to allow
passage across the hydropower facility within
a reasonable length. For open canoes, a
maximum drop or around 1 ft is suggested
(Caisley and Garcia 1999). A maximum drop
height of 4 ft is recommended before a
physical model study is necessary (Colorado
Water Conservation Board 2008). This
constraint may be relaxed if the passage
module is designed for a higher level of
difficulty
L
D-13
Table 24. Recreation passage module design constraints (continued)
Constraint Formalization
Scale
(L= Local,
G = Global)
Limit the maximum velocity of water in
the module
The maximum velocity in the module will be
related to the flow rate and slope through the
module. For destination whitewater type
courses, velocities of less than 15 ft/s are
recommended (Simmons et al. 1977). Lower
velocities are required for modules where
novice boaters are expected
L, G
D.6 DESIGN ENVELOPE SPECIFICATION
The human element of recreation passage entails safety as the primary design consideration. The mere
presence of a recreation passage module reassures those in small craft that they can travel downstream
with minimal risk of harm, capsizing, or drowning. Low-head hydraulic structures are notorious for
creating unstable and fatal conditions; and extreme caution, foresight, and engineering expertise must be
included in any recreation passage module design.
Recreation passage can also significantly enhance the multipurpose value proposition of an SMH facility
by providing tourists and recreational enthusiasts with a unique instream experience. Recent boat chutes
and water parks in Texas,13
Colorado,14
and the United Kingdom15
have received positive feedback from
stakeholders. These examples demonstrate the value of incorporating recreation passage into the design
phase, either as a challenging water feature or as a simple conveyance structure. Although these designs
have been incorporated into existing non-powered low-head dams, the inclusion of recreation passage
module–type facilities into small hydropower projects remains largely untested in practice. However, the
requirements, constraints, and measures of performance laid out above are intended to create a bounded
envelope for recreation passage module design innovation. Their implications can be summarized as
follows:
A recreation passage module can be designed with varying degrees of difficulty.
Hydraulics and safety provisions must be appropriately matched to the desired type and difficulty of
passage.
Recirculating hydraulic jumps must be avoided under a range of flow conditions.
Safe passage must be paramount under all flow conditions.
The basic geometry of the stream and flow conditions should be known.
Module cost and size should be optimized within the budget of a facility—longer passage modules
help create appropriate passage hydraulics, although they require more materials and a longer
foundation module, which will add cost.
Module cost and operational flexibility should be optimized within the budget of a facility—the
module intake must effectively pass a range of discharges while safely conveying recreationists
downstream.
The inclusion of natural features is desirable.
13
http://www.mysanantonio.com/news/environment/article/Mission-Reach-is-open-to-paddling-
4042020.php#photo-3726992 14
http://www.chaffeecountytimes.com/free_content/redesign-of-silver-bullet-rapid-may-benefit-both-boaters-
and/article_cb687376-a49e-11e3-a47e-0017a43b2370.html 15
http://www.medwaycanoetrail.co.uk/trail.php
D-14
D.6.1 State-of-the-Art Advances
Novel designs in the United Kingdom have addressed the combined needs of upstream fish passage and
downstream recreational passage through a single sloping chute structure (Figure 40). In these designs,
artificial brushes are used to dissipate flow energy to create favorable conditions for fish and boats. One
such structure, constructed using reinforced concrete and polysterene void formers to reduce the
deadweight of concrete, was designed and installed in an existing bypass channel in less than 12 weeks at
a cost of roughly $120,000 (2010 £80,000).
A series of recreation chutes and slides on the River Medway in the United Kingdom have been
incorporated into existing low-head dams (Figure 41). Many of these concrete structures are designed
with steep gradients and low flows to enable consistent passage of canoes and kayaks. Flow control is
achieved through the use of a regulating gate on the opposite side of the stream. This arrangement applies
physical separation to ensure that dangerous, recirculating hydraulics do not occur near points of passage.
Figure 40. Combined canoe and fish pass in the United Kingdom. Both are constructed with a 1:6 gradient.
(Photo courtesy of the UK Environment Agency and CH2M)
D-15
Figure 41. Canoe/kayak slide adjacent to a fish passage structure located at a gated weir. This canoe pass is the
steepest gradient in the Medway canoe pass system. A gated weir can be seen on the right, while a canoe/kayak slide
can be seen left-of-center. A fish passage channel can be seen to the left of the canoe/kayak slide. (Photo courtesy of
the UK Environment Agency)
D.6.2 Research Gaps
Compared with fish passage, there are a very limited number of public studies, reviews, or design criteria
for recreation passage at low-head hydropower facilities. Those present in the literature are generally
focused on a single design at a single site, most often at a weir or non-powered dam. Although many of
these reports strive to offer general design guidelines, the systematic development of important functional
relationships for recreation passage design is a significant research gap.
The need for recreation passage modules at small hydropower dams is apparent, as is the need for
additional research. Major research gaps include the following:
Cost—The biggest challenge from a design perspective is anticipated to be cost. Recreation modules
must mitigate the abrupt drop necessary for hydropower generation with a gradient acceptable for
passing small watercraft. As head increases, the length of the module must grow disproportionately,
adding not only to the module cost itself but also to the cost of a supporting foundation. The length of
the module is generally unknown, and historically a model study has been used to estimate the
tailwater elevation and backwater profile that create safe hydraulic conditions.
The use of physical modeling and numerical simulations—In designing recreation passage structures,
the current approach is to use customized physical model tests and simulations to analyze the overall
hydraulic behavior of the structure; conditions that create a hydraulic jump; the need for and type of
inlet control structure; the behavior of in-module structures that dissipate energy, slow the flow, and
generate eddies; and conditions that lead to scour downstream. This approach is born out of both the
D-16
lack of general design guidelines for a variety of recreation passage types, and the importance of
mitigating personal safety risks. Recreation passage module designs will require the use of simulation
and testing capabilities to improve their concept viability.
Trade-offs between simplicity of design, safety, and aesthetics—Many existing boat chutes and other
recreation passage structures are made of concrete, which enables simplicity of design, stability, and
endurance, although it generally does not match the surrounding aesthetic. The use of boulders and
natural materials may help the module blend into the surrounding environment, although sharp edges
and irregular and protruding surfaces increase the complexity of in-module hydraulics and may
compromise public safety. Additional research is needed to develop modules that incorporate a natural
aesthetic while enabling simplicity of design.
Desirable degree of difficulty—SMH facilities have the potential to create unique recreation
opportunities with varying degrees of difficulty. It is unclear what level of difficulty will be generally
accepted by stakeholders and, consequently, should be targeted by designers. Increased difficulty will
generally mean steeper gradients, which may reduce overall material costs but increase the need for
safety mitigation measures.
E-1
APPENDIX E. WATER PASSAGE MODULE
Water is the primary resource for energy generation in a hydropower facility. In a strict sense, any flow
not used for generation represents a reduction in revenue for the project. However, there is a need to pass
water for non-generating purposes. Flood flows in excess of generation capacity must pass safely
downstream to minimize upstream flooding and to avoid compromising the stability of the facility. Water
is allocated toward fish, sediment, and recreational craft passage structures when needed (see Appendices
B, C, and D of this report). Environmental minimum flows are passed through small turbines or conveyed
over hydraulic structures to minimize the degradation of downstream fish habitat and river morphology
and to mitigate adverse impacts on recreation. Furthermore, the water quantity and quality requirements
for uses downstream of the hydropower facility—such as public consumption, irrigation, fishing,
commercial use, waste treatment plants, and cooling plants—must be met in conjunction with generation
needs. When water cannot flow elsewhere through the facility, it must flow over a water passage module.
E.1 OBJECTIVES
To minimize the effects of the disruption in the continuity of water passage due to the presence of an
SMH facility on a waterway, non-generating water must be transported across the SMH facility. The
primary technical objective of the water passage module of the SMH facility is to allow the conveyance
of non-generating water through the facility.
To achieve the overall primary technical objective, the water passage module needs to achieve the
following specific objectives (Figure 42):
1. Safely pass flows not usable by the generation module.
2. Support entrance hydraulics for the generation module.
3. Meet the water supply demands and the hydraulic requirements of other uses, such as human water
supply, irrigation, commercial supply, wastewater treatment plants, and cooling plants.
4. Maintain hydraulics for sediment passage through the hydropower facility and sediment transport
capacities downstream of the hydropower facility.
5. Maintain hydraulics for fish passage through the hydropower facility and for fish habitat upstream
and downstream of the hydropower facility.
6. Maintain hydraulics for recreation passage and maintaining recreation quality downstream of the
hydropower facility.
7. Integrate structurally into foundation module.
Water Passage Module Primary Technical Objective
Allow the conveyance of non-generating water through the SMH facility
E-2
Figure 42. Conceptual schematic of the specific objectives of a water passage module.
E.2 REQUIREMENTS
The requirements for the water passage module are quantifiable characteristics or behaviors that the water
passage module must exhibit to ensure its successful operation. Meeting these requirements ensures that
the water passage module will achieve its specific objectives and thereby its primary technical objective.
The requirements for the water passage module are summarized in Table 26, Table 27, and Table 28,
where they are characterized as Functional, Performance, Interface, and Other, similar to the functional
requirements of the fish, sediment, and recreation passage modules (Appendices B.2, C.2, and D.2,
respectively). Furthermore, in these tables, the relationship of each requirement for the water passage
module with the five constituents of the river continuum—water, sediment, energy, organisms and
nutrients—is indicated in an analogous manner to the requirements for the other passage modules
(Appendices B.2, C.2, and D.2, respectively). In Table 26, Table 27, and Table 28, the water passage
module requirements are grouped by its specific objectives to indicate the close association between the
water passage module requirements and specific objectives.
E-3
Table 26. Water passage module requirements. In the fourth column: F = Functional; P = Performance; I =
Interaction; O = other. In columns 6–11, an “X” denotes a relationship to the river continuum constituent indicated
in the top row
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter q
ua
lity
1 Safely pass flows not usable
by the generation module
a
Route flows around the
generation module to
appropriately sized water
passage modules
F, I
Flows that cannot be used by
the generation module should
be passed downstream to
prevent overtopping of the
SMH facility
X X
2 Support entrance hydraulics
for the generation module
a
Partition flows between the
water passage module and
the generation module
F, I
The generation module will
require a consistent flow of
water to ensure reliable and
efficient operation. The water
passage module should be
designed to ensure flows are
smoothly passed to the
generation module under
normal, low, and high water
conditions.
X X
b
Maintain sufficient head and
intake submergence for the
generation module
F, I
The generation module intake
should remain submerged to
avoid head losses, and the
head above the intake should
be maintained within the
design range of the generation
module to ensure reliable and
efficient power production.
3
Meet the hydraulic
requirements for other
multipurpose water uses,
such as water supply,
irrigation, wastewater
treatment, and cooling water
a
Route river flow to water
passage structures designed
to pass a predetermined flow
to meet demand
F, P
Water should be routed to a
water passage structure that
supplies the required flows
downstream
X X
b
Maintain hydraulic
conditions required for
supplying these uses
F, P
In addition to the amount of
water flow, many uses, such as
cooling intakes, require certain
ranges of depth or flow
velocity downstream of the
facility, which must be
satisfied
X X
E-4
The water passage module will consist of suitable structures to allow a portion of the flow to bypass the
SMH facility, including spillways, weirs, and bypass channels. These structures will need to have intakes
or crests that are appropriately sized to route the expected discharges (USBR 1977). For instance, an
orifice used to convey non-generating flows downstream must have a sufficient diameter to allow the
necessary discharges through the SMH facility. A broad-crested weir must have a length designed to pass
non-generating flows. An important requirement is that the water passage module must allow the
conveyance of predetermined discharges for a range of flow conditions; a stage-discharge relationship
quantifying the volume of discharge to be passed for a given water depth during both the low and high
flow levels expected at the SMH facility must be developed.
Many downstream water uses require that specific flow hydraulics be maintained around intakes to ensure
the undisturbed operation of these facilities. Intakes for certain facilities, such as pumping stations,
require a minimum level of submergence, which in turn requires maintaining a minimum required flow
depth of the river (Yildirim and Kocabac 1995; Werth and Frizzel 2009). Other types of intakes may
require the flow velocity or bed shear stress around the intake to be within certain ranges to prevent
excessive scour (Maclean 1991; Nakato and Ogden 1998). The water passage module needs to account
for the requirements of these various uses and supply water to fulfill them. It is likely, however, that the
requirements of some of the various uses will conflict with one another; and it may not be feasible for all
of them to be entirely satisfied. Therefore, a site assessment should be performed to establish acceptable
performance levels to satisfy each type of water use.
During flood conditions, it is possible that the amount of water flow will exceed what the generation
module can safely use. The excess water flow, especially during more extreme flood events, may overtop
the SMH facility, threatening its stability. The water passage module must be able to convey any excess
flood discharge safely downstream to prevent its compromising the stability and safety of the SMH
facility. To ensure its capability to do so, the sizes of the water passage structures making up the water
passage module must be appropriately selected so that they can handle these water flows.
As discussed in Appendix C, a suitable amount of water flow must be diverted to the sediment passage
module to ensure the transport of sediment across the SMH facility. The water flow required by the
sediment passage module to achieve its primary technical and specific objectives must be supplied by the
water passage module (Table 27). This requirement entails that an interface between the water and
sediment passage modules must be established in the SMH facility to ensure seamless operation of the
sediment passage module. Furthermore, the presence of hydropower facilities is known to reduce the
downstream competent flows required for transporting sediment (Brandt 2000; Graf 2006; Schmidt and
Wilcock 2008; Magilligan et al. 2013). Researchers have documented that disruption of the stream
competence often leads to undesired morphologic changes, such as armoring, channel narrowing, and
excess bank erosion (Appendix C). To minimize such changes, the water passage module must allow
flows through the SMH facility that are competent to transport the range of sediment sizes encountered at
the SMH facility (Table 27).
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Table 27. Water passage module functional requirements. In the fourth column: F = Functional; P =
Performance; I = Interaction; O = other. In columns 6–10, an “X” denotes a relationship to the river continuum
constituent indicated in the top row
An important requirement for the water passage module is that it control the amount of suspended
sediment transported within the water column downstream of the SMH facility. Suspended sediment is a
key contributor to poor water quality; and its contributions to reducing water clarity, hindering water
treatment, and impacting the health of aquatic organisms are well documented (Davies-Colley and Smith
2001; Owens et al. 2005; Bilotta and Brazier 2008). In addition, suspended sediments often transport
contaminants such as heavy minerals, phosphorus, and nitrogen, which may be harmful to humans as well
as to other organisms. Therefore, the flow conditions downstream of the SMH should promote the settling
out of suspended sediment and minimize its resuspension (Table 27). At the same time, excessive settling
of fine sediment promotes river aggradation and fine sediment intrusion into the river bed, which degrade
fish habitat spawning gravels (Sear 1993; Kondolf 2000;). Therefore, the flow conditions downstream of
the SMH facility need to be controlled by the water passage module so that the conflicting requirements
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter q
ua
lity
4
Maintain hydraulics for
sediment passage through the
hydropower facility and
sediment transport capacities
downstream of the
hydropower facility
a Supply water to sediment
passage module F, I
A portion of the river flow
may be routed to the sediment
passage module to transport
sediment through the SMH
facility. This portion is not
used by the generation module
X X X
b
Maintain hydraulic
conditions for controlling
suspended sediment transport
downstream of the SMH
facility
F, P
Maintaining water quality
requires reductions in
suspended sediment
concentrations, which are
triggered by allowing
suspended sediment to settle.
Excessive suspended sediment
settling, however, degrades
fish habitat and accelerates
river geomorphic change
X X X X
c
Provide sufficient water
flows for achieving sediment
transport capacities that
minimize geomorphic change
downstream of the
hydropower facility
F, P
To minimize geomorphic
changes (e.g., aggradation,
lateral migration) in the river
downstream of the hydropower
facility due to the disruption in
the river flow connectivity
caused by the SMH facility,
flows need to be released to
transport sediment downstream
of the facility
X X X
E-6
are reconciled. Appropriate measures of performance, examined in Appendix E.5, should be established
to quantify the degree to which each of these requirements is satisfied.
In addition, as noted in Appendix B.2, the water passage module needs to supply the fish passage module
with water to maintain flow conditions that allow the fish passage module to achieve its specific and
primary technical objectives (Table 28). As in the case of the sediment passage module, an appropriate
interface between the fish passage and the water passage modules should be present to ensure that the
appropriate flows are diverted to the fish passage module. At the same time, the water passage module
must pass enough water to maintain fish habitat downstream of the SMH facility. As discussed in
Appendix B, acceptable fish habitat requires certain mean and turbulent flow characteristics, including
minimum flow depth, maximum velocity ranges, bed slope, and turbulence levels (Table 11). The water
passage module therefore is required to convey sufficient flow discharge downstream to satisfy these
requirements for maintaining acceptable fish habitat quality (Dermisis and Papanicolaou 2009; Reinfelds
et al. 2010; Noonan et al. 2012).
Similar to the sediment and fish passage modules, the recreation passage module need to be supplied with
water to achieve its primary technical objective of passing recreational craft through the SMH facility
(Table 28). Therefore, an important requirement for the water passage module is to interface with the
recreational passage module and supply the necessary water flows, as determined in Appendix D of the
present report. In addition, the water passage module is required to supply sufficient flows downstream of
the facility to maintaining the hydraulics necessary to recreation. For example, recreational craft have
specific depth and flow discharge requirements for different recreational activities, such as kayaking and
whitewater rafting (Vandas et al. 1990, BLM 2016). At the same time, an additional requirement for the
water passage module is to minimize the likelihood of occurrence of excessive flow velocities that might
compromise the safety of recreational craft.
Table 28. Water passage module functional requirements. In the fourth column: F = Functional; P =
Performance; I = Interaction; O = other. In columns 6–10, an “X” denotes a relationship to the river continuum
constituent indicated in the top row
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter q
ua
lity
5
Maintain hydraulics for fish
passage through the
hydropower facility and for
fish habitat upstream and
downstream of the
hydropower facility
a Supply water to the fish
passage module F, I
A predetermined amount of
water should be diverted to the
fish passage module to allow
fish migration along the river.
This portion is not used by the
generation module
X X
b
Provide sufficient water
flows for maintaining fish
habitat hydraulics upstream
and downstream of the
hydropower facility
F, P
Predetermined flows need to
be passed downstream to
maintain fish habitat
conditions and prevent loss of
biodiversity
X X
E-7
Table 27. Water passage module functional requirements (continued)
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Rec
rea
tion
Wa
ter q
ua
lity
6
Maintain hydraulics for
recreation passage and
maintaining recreation
quality downstream of the
hydropower facility
a Supply water to the
recreation passage module F, I
A predetermined amount of
water needs to be diverted to
the recreational passage
module to allow recreational
craft to pass through the
hydropower facility. This
portion is not used by the
generation module
X
b
Maintain hydraulics for
recreation quality
downstream of the
hydropower facility
F, P
The use of recreational craft
downstream of the
hydropower facility may
require certain ranges of depth
and flow velocity, which must
be satisfied for the crafts
encountered
X X X X
7 Integrate structurally into
foundation module
a
Transmit all forces through
non-critical components into
the foundation module
F, P, I
The water passage module will
be supported instream by a
foundation module that serves
as an interface to the
streambed
X
E.3 INPUTS, FUNCTIONAL RELATIONSHIPS AND PROCESSES
This section identifies the processes that govern the operation and behavior of the water passage module.
These processes are quantified with functional relationships, which are also listed in this section for the
water passage module. Knowledge of these processes and functional relationships is a prerequisite for
understanding the function and predicting the behavior of the water passage module. Therefore, the
functional relationships provide the basis for the water passage module design, so that it accomplishes its
primary and secondary technical objectives. Before examining the water passage module functional
relationships, it is important to identify the key variables, which are the inputs to these functional
relationships.
E.3.1 Necessary Inputs
The key variables that are inputs to the water passage module functional are presented in Table 29. These
variables are divided into five categories, depending on their relation to sediment, flow, geomorphologic
E-8
or chemical processes, or geometry. This categorization further allows systematic investigation of the
functional relationships to which these inputs relate.
Table 29. Water passage module necessary inputs
Identification of
key inputs Formalization
Flow variables
Range of flow discharges encountered, watershed hydrologic
characteristics, climate, land use/land cover, flow depth, turbulent
shear stress, water temperature, friction factor, flood frequency and
magnitude, tailwater depth, flow needs of other modules, flow needs of
other multipurpose uses
Geometric variables
Geometry and shape of passage module, elevation difference upstream
and downstream of facility, passage module slope, passage module
length, stream cross-sectional geometry upstream and downstream of
SMH facility, geometry of other modules
Geomorphologic variables River bed slope, bed topography, friction factor, channel sinuosity,
bank geometry, bank soil composition
Sediment characteristic variables
Sediment grain size distribution (e.g., median grain diameter,
geometric standard deviation), friction factor, sediment fall velocity,
sediment angularity, sediment shape, relative protrusion, suspended
sediment concentration
E.3.2 Functional Relationships
The functional relationships related to the operation of the water passage module, along with a brief
statement of the importance of each one, are tabulated in Table 30. The river flow discharge at the
location of an SMH facility is intimately related to the water surface runoff, which is the amount of water
from precipitation, snowmelt, or other sources that does not infiltrate into the soil but is conveyed into the
river (Figure 43). The surface runoff in a watershed is a function of the watershed hydrologic
characteristics, including the climatic conditions at the watershed, the watershed drainage area, the land
use and land cover of the watershed, its topography, and its soil type (Maidment 1993; Papanicolaou and
Abban et al. 2016). The most important climatic condition influencing surface runoff and thus river flow
is precipitation, which quantifies the amount of water contributed to the watershed by the rainfall. It is
often characterized by the rainfall intensity, which is the volume of precipitated water per unit of time, the
duration of rainfall, and its distribution over the watershed. It is well documented (Figure 44) that river
discharge is related via a power functionality to the drainage area of the watershed, with larger watersheds
yielding higher river discharges (Maidment 1993; Mulvihill and Baldigo 2012).
Table 30. Functional relationships governing water passage module operation
Relationship of To Rationale/importance
Flow discharge
1. Watershed
contributions
2. Passage module
geometry
3. Available head
4. Tailwater elevation
The flow rate that needs to be passed depends on the flow that is
conveyed by the river upstream of the SMH facility, which
depends on the contributing watershed characteristics. The flow
rate that can be passed through the SMH facility is dependent on
the size of the passage structure (e.g., weir, spillway) and the
available head
Flow velocity
downstream of
facility
Flow discharge,
slope, friction factor,
river cross-sectional
geometry, river
geomorphology,
grain size distribution
The flow velocities downstream of the hydropower facility are
predominantly a function of the flow rate conveyed, and the
river cross-sectional geometry, which dictates the available flow
area. The river bed morphology as well as the sizes of the
sediment grains making up the river bed, determine the friction
factor, which is a measure of the bed the resistance to the flow
E-9
Table 29. Functional relationships governing water passage module operation (continued)
Relationship of To Rationale/importance
Flow depth
downstream of
facility
Flow discharge,
slope, friction factor,
river cross-sectional
geometry, river
geomorphology,
grain size distribution
Similar to the flow velocity, the flow depth at a river cross-
section depends on the flow discharge and river cross-sectional
geometry. Flow depth also depends on the resistance to the flow,
which is governed by the river geomorphology and the sizes and
types of the river bed material
Turbulence
characteristics
downstream of
facility
Flow discharge,
slope, river
geometry, river
geomorphology,
grain size distribution
Turbulence is generated broadly from the interaction of the
mean flow with the roughness elements on a river bed. As a
result, the turbulent flow patterns are governed from the mean
flow quantities, e.g., flow discharge, velocity, depth, and the
river geomorphologic characteristics, such as river slope, bed
sediment sizes and the presence of large-scale geomorphologic
features such as bedforms
Sediment transport
capacity
Flow discharge, flow
depth, bed slope,
grain size distribution
The capacity for transport of expected sediment loads stems
from the balance between flow shear and resisting forces. The
former are dependent broadly on flow discharge, depth and
slope, whereas the latter are dependent mostly on the sediment
sizes to be transported, the interaction between these sizes, and
the large-scale geomorphology of the river, e.g., the existence of
bedforms
Suspended sediment
concentration
1. Mean flow
characteristics and
patterns
2. Turbulent flow
characteristics
3. Supplied sediment
4. Settling velocity
1. The mean flow velocity is the main driver for the
transportation of suspended sediment downstream
2. Turbulence causes diffusion and mixing of the transported
sediment concentration
3. The amount of sediment transported downstream in
suspension is dependent on the amount of sediment supplied
from upstream
4. The sediment settling velocity quantifies the tendency of
sediment to deposit or remain in suspension.
Figure 43. Dependence of the bankfull discharge on the watershed drainage area for different hydrologic
units in New York state. (Mulvihill and Baldigo 2012)
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Figure 44. (a) Example of a typical hydrograph indicating the flow response (blue curve) to precipitation
(gray bars). (b) Example hydrograph for the past 9 years for the Clinch River near Tazewell, Tennessee.
The topography of the watershed also plays an important role in surface runoff. Typically, the effects of
the watershed topography are considered through the average slope of the watershed and a characteristic
length, which is representative of the watershed shape and quantifies the average distance that water must
travel within the watershed before reaching the river. For instance, watersheds with more elongated
shapes tend to yield smaller river discharges, as water needs to travel further before reaching the river.
Furthermore, the land use and land cover of the watershed play an important role, as they determine the
amount of precipitation that infiltrates into the soil and does not generate runoff. The presence of denser
vegetative cover minimizes infiltration and accelerates water runoff. The presence of impervious surfaces,
such as paved roads and buildings, effectively eliminates infiltration, thus increasing surface runoff and
river discharge. Along the same lines, the type of soil in the watershed controls water infiltration and
therefore the amount of runoff. Soils with higher clay content exhibit smaller infiltration and therefore
higher runoff.
The variability in climatic conditions, land use, land cover, and soil type in a watershed leads to temporal
variations in surface runoff and thus in river flow. This temporal variability in water flow is depicted by
the flow hydrograph (Figure 44a), which gives the river discharge at a point along the river as a function
of time. The construction and analysis of hydrographs allow a determination of the flood magnitude and
frequency at the location of the SMH, which in turn allows prediction of the flows that will be
encountered by the SMH facility (Figure 44b).
E-11
The water passage module typically consists of a water conveyance structure, such as a spillway, an
orifice, or an open channel (USBR 1977). For all these types of structures, the flow discharge that can be
conveyed across the structure is a function of the available head, which is the difference between the
water surface elevations upstream and downstream of the conveyance structure (Chaudhry 2008). In
general, for a weir-type device, the flow, Q, and water levels or head, h, are generally related as follows:
𝑄 ∝ 𝑓(𝐺, 𝐶, ℎ𝑎) . (E.1)
The parameter G refers to the geometry of the mechanism structure used to pass flow, such as the width
of a sill over which flow passes (for a weir-type device), length over which the flow passes (for a weir-
type device), width of channel, slope, and bed roughness (for open channel flow), or diameter of conduit
(for a conduit flow). The parameter C is a coefficient used to align empirical formulations with actual
flow.
In the case of a spillway, for example, the conveyed discharge is a function of the shape of the spillway
weir and the spillway length. The dependence of the conveyed spillway discharge on the weir shape is
depicted by the discharge coefficient (Figure 45). For orifices and open channels used for passing water,
the discharge through the structure is a function of the structure cross-sectional geometry, slope, and bed
roughness. Knowledge of these characteristics allows the prediction of the discharges that can be
conveyed through the orifice or open channel. Conversely, these functional relationships allow estimation
of the structure dimensions required to allow the conveyance of a given discharge.
Figure 45. Relationship between the weir discharge coefficient (vertical axis) and
the available water head (horizontal axis) for an ogee-shaped weir. (USBR 1977)
Downstream of the SMH facility, the prevailing flow depth in a river is a function of the discharge—
which in this case is controlled by the water passage module of the SMH facility—as well as of the river
bed slope, the cross-sectional geometry of the river, and the resistance that the flow encounters on the
river bed and banks. The resistance of the river bed and banks to the flow has long been an object of
study. This resistance has typically been quantified by the friction factor, which has been related to a
E-12
characteristic length scale representative of the sediment sizes making up the bed. However, the friction
factor is also a function of the relative submergence, which expresses the ratio of the flow depth to the
characteristic height of the sediment making up the bed. For most rivers, the relative submergence is
larger than one, indicating that the river bed material is deeply submerged. For such cases, the friction
factor depends only upon the characteristic bed sediment height. However, in rivers with large boulders
and other large bed features, such as sand dunes, it is possible that the diameters of these elements may
become comparable to or even larger than the flow depth, so that they may protrude through the water
free surface. This is a condition known as “low relative submergence,” where the friction factor increases
significantly and becomes also a function of the relative submergence ratio (Millar 1999; Ferguson 2007;
Rickenmann and Recking 2011). The flow velocity is a function of the discharge and the cross-sectional
area of the flow, which is in turn a function of the flow depth, width, and shape of the cross-sectional
area. Therefore, the flow velocity is directly related to the same parameters that determine the flow depth.
Broadly, turbulence is produced by the interaction of high-speed fluid with the roughness elements that
make up the river bed (Nezu and Nakagawa 1993; Strom and Papanicolaou 2007; Hardy 2011; Detert et
al. 2010). This interaction of the flow with the roughness element leads to the generation of vortices
around these roughness elements, which increase the turbulence levels in their vicinity. Some research has
shown (Shamloo et al. 2001; Sadeque et al. 2008; Lacey and Rennie 2011; Papanicolaou et al. 2012) that
different vortices form under different relative submergence regimes, and that the relative submergence
also affects the turbulence levels of the flow. At the same time, the levels of turbulence in the flow
depend on the bulk flow characteristics, including the flow velocity and therefore the flow discharge, flow
depth, and bed slope.
Although the primary technical objective of the water passage module is the conveyance of water rather
than sediment through the SMH facility, it provides the water supply required for the transport of
sediment in the river reaches downstream of the SMH facility. It is pertinent, therefore, to briefly outline
the key functional relationships that govern the transport of sediment to the extent that they relate to
sediment transport in the context of the water passage module specific objective. In general, coarser
sediment is transported in proximity to the bed and constitutes the bedload (Yalin 1977). As discussed in
detail in Appendix C of this report, the bedload transport capacity is typically expressed as a function of
the difference in the force applied by the flow and the threshold force required to set a coarse sediment
grain of given size in motion (Yalin 1977). The applied flow force, also called “bed shear stress,” is a
function of the flow depth, the river bed slope, and the density and the sizes of the sediment grains to be
transported. The threshold stress, or critical bed shear stress for incipient motion, is broadly dependent on
the heterogeneity of the bed material grains, their packing density, their shapes, and the degree to which
they protrude into the flow (Yalin 1977; Wiberg and Smith 1987; Papanicolaou et al. 2002). Finer
sediment, on the other hand, is typically transported in suspension. The suspended sediment is considered
to settle out of suspension and deposit when a characteristic velocity length scale of the flow called
“friction velocity” is less than the settling velocity of the suspended sediment. The flow shear velocity
depends on the flow depth and bed slope within the water passage module, while the fall velocity is
determined from the sediment size and water temperature (Raudkivi 1998).
E.4 MEASURES OF MODULE PERFORMANCE
Assessing the efficiency of the water passage module in meeting the requirements listed in Appendix E.2
requires a set of quantifiable indices (Table 31). The indices will, in turn, allow evaluation of the
efficiency with which the water passage module accomplishes its specific and primary technical
objectives.
E-13
Table 31. Water passage module measures of performance
Index Status
Index of Hydrologic Alteration More research and modeling needed
Indices of Schmidt and Wilcock (2008) Limits available—modeling needed
Indices of Grant et al. (2003) Limits available—modeling needed
River width Limits available
Flow depth Limits available
Flow velocity Limits available
Bed slope Limits available
Turbulence kinetic energy Limits available
Energy dissipation function Limits available
Suspended sediment concentration Limits available
Subsurface flow hydraulic gradient Limits available
River bed sediment and suspended sediment size distribution Limits available
The most comprehensive suite of indices for assessing the effects of hydropower facilities on the
hydrology of a river is the Indicators of Hydrologic Alteration (IHA) (Richter et al. 1996; Magilligan and
Nislow 2005; Magilligan et al. 2013) The IHA considers 32 hydrologic variables that quantify the
alterations caused by the SMH to five aspects of the hydrologic regime: (1) magnitude of monthly flow
conditions; (2) magnitude and duration of annual water conditions; (3) timing of annual extreme
conditions; (4) magnitude duration and frequency of pulses in river flow; and (5) rate at which hydrologic
conditions change. Summary statistics for these variables are compared for periods before and after the
installation of the SMH facility to allow assessment of the impacts of the SMH facility. To assess the
performance of water passage module designs before the placement of an SMH facility, the hydrology in
the post-construction period would need to be projected via the SMH simulation capability.
Assessment of the water passage module performance with respect to maintaining sufficient sediment
transport capacity in the river reaches downstream of the SMH facility needs to involve measures
quantifying the river geomorphic change. Such measures are the three indices proposed by Schmidt and
Wilcock (2008), which quantify (1) the potential for river aggradation or degradation, (2) the bed incision
potential, and (3) the magnitude of flood reduction under the conditions before and after the installation of
the SMH facility. As discussed in Appendix D.4, acceptable limits for these indices are provided by
Schmidt and Wilcock (2008), who compile ranges of values for the three indices for hydropower facilities
with minimal geomorphic changes. Alternately, the simpler two indices of Grant et al. (2003) could be
used; they are expressed by (1) the ratio of the sediment supply upstream and downstream of the SMH
facility and (2) the ratio of the fractions of sediment-transporting flows before and after the placement of
the SMH facility. As in the case of the IHA, the indices of Schmidt and Wilcock (2008) and of Grant et
al. (2003) require knowledge of key input variables following the installation of the SMH facility. Ranges
of their values for this condition can be obtained through the simulation capability of the SMH.
For assessing fish habitat hydraulics in the river reaches downstream of the SMH facility, the optimal
metrics are the ones considered for the assessment of the fish passage module (Appendix B.4). These
metrics include the flow depth, flow velocity, TKE, and EDF (OTA 1995; Maxwell and Papanicolaou
2000; Liu et al. 2006; Dermisis and Papanicolaou 2009). In addition, the suspended sediment
concentration could be a useful measure for assessing the amount of infiltration of suspended sediment in
the natural stream beds downstream of the SMH facility. A more rigorous method is proposed by Kondolf
(2000), which considers the grain size distribution of the river bed material and of the fine sediment as
well as the hydraulic gradient for subsurface flow.
The performance of the water passage module with respect to the recreation quality and water supply for
various uses downstream of the SMH facility can be assessed by considering the flow depth, discharge
velocity, and flow velocity in the river reaches downstream. Finally, the performance of the water passage
E-14
module for maintaining water quality in the downstream reaches can be assessed by considering the
suspended sediment concentration, for which limits are available from the Environmental Protection
Agency (EPA 2016).
E.5 DESIGN CONSTRAINTS
The analysis of the water passage module requirements (Appendix E.2) in conjunction with the functional
relationships (Appendix E.3) allows the specification of design constraints for the water passage module
(Table 32). These are considered the behaviors and features that the water passage module must exhibit to
accomplish its primary technical objective of conveying non-generating flows across the SMH facility. At
present, strict quantitative criteria are not specified for each of the design constrains, as the development
of such criteria is beyond the scope of the present document. Instead, the identifications of the water
passage module performance measures outlined in Appendix E.4 are used as initial building blocks for
formalizing technical design constraints. The design constraints examined in Table 32 are characterized as
local when they pertain specifically to the water passage module and global when their validity can be
extended to the other modules of the SMH facility.
Table 32. Water passage module design constraints
Constraint Formalization/rationale
Scale
(L= local,
G = global)
The water passage module must be
able to intake water for a range of
conditions
The water passage module must be able to intake
water for conveyance downstream for a range of
approach flow conditions upstream of the SMH
facility
L
The water passage module must
convey enough water flow
downstream to meet the demands for a
variety of uses
There are a variety of uses, such as human
consumption, industrial use, cooling plants, and
wastewater treatment plants, that must be satisfied;
and none of these uses may be excluded
L
The water passage module must be
able to pass flood flows to prevent
overtopping of the SMH facility
Failure to pass flood flows may lead to overtopping
of the SMH facility and compromise of its structural
stability
L
The water passage module must be
able to convey flows sufficient to
prevent significant river
morphological changes
The flows conveyed by the water passage module
must ensure sufficient transport capacity in the
downstream river reaches to prevent significant
alterations in the river morphology
L
The flow discharge conveyed must
maintain fish habitat in the
downstream river reaches
The flows conveyed by the water passage module
must ensure acceptable ranges of flow depth,
velocity, and turbulence, and minimize fine
sediment intrusion into spawning gravels
L
The water passage module must
successfully interface with the fish,
sediment, and recreation passage
modules
The water module must be able to supply the other
modules with sufficient water to achieve their
primary technical objectives G
E-15
Table 31. Water passage module design constraints (continued)
Constraint Formalization/rationale
Scale
(L= local,
G = global)
Module components cannot be heavier
than the lift capacity of available
cranes and transport vehicles or
vessels
The module components must not exceed the
capacity of transport vehicles or vessels and
available cranes so that they can be transported to
the SMH site and placed
G
Module components cannot exceed in
size the size of available transport
vehicles or vessels
The module components must be smaller than the
transport vehicle or vessel to allow their
transportation to the SMH site
G
Module components must be
compatible with one another
The module components must connect with one
another and offer structural stability to the module. G
Module components must be
compatible with foundation modules
The module components must be compatible with
the foundation module to ensure the structural
stability of the module from the SMH facility
foundation
G
Module components must be able to
withstand the water forces under
conditions of flood
Because the water passage module needs to convey
flood discharges, it must be able to withstand the
forcing caused by the flood water
G
E.6 DESIGN ENVELOPE SPECIFICATION
The systematic examination of the water passage module for an SMH facility in this section has generated
a list of design constraints for the water passage module, the fulfillment of which ensures that the water
passage module accomplishes its primary technical objective of conveying non-generating flows across
the SMH facility. As is the case for the other modules of the SMH facility, the design constraints
identified in Table 32 may alternately be viewed as a design envelope for characteristics and behaviors
that a successful water passage module design must exhibit to accomplish its primary technical objective.
Note that multiple water passage module designs could fulfill these design constraints, but it is not the
goal of the present report to identify the optimal design. To identify the optimal designs for the water
passage module, the present report provides measures, identified in Appendix E.4, that allow assessment
of the performance of potential designs and identification of the optimal design.
Specification of the water passage module design envelope requires the identification of limits for the
water passage module performance measures provided in Appendix E.4. Identification of these
performance measure limits allows the exclusion of potential water passage module designs that do not
perform within the identified limits. For instance, a design for the water passage module that allows water
to overtop the SMH facility during a possible flood condition cannot be considered. Identification of such
performance measure limits is tied to specific characteristics at the SMH facility site, including the
hydrologic regime of the watershed in which the SMH facility site is located. It is possible to classify
potential SMH sites with respect to some key, recurring characteristics, such as the watershed hydrology,
that are pertinent to the design envelope specification of the water passage module. Similarly, potential
SMH sites will need to be classified in terms of the types of sediments (coarse vs. fine) and fish species to
derive water passage module designs that are optimal for the specific sediment and fish species common
in a class of SMH sites. The outcome of such classification schemes will be the establishment of limits
and designs that are applicable to a class of SMH sites with similar characteristics, thereby enhancing
SMH standardization. Site classification is therefore of paramount importance to identifying the limits of
the water passage module design envelope.
The concept of scale is particularly important for the water passage module, as the water conveyed by the
water passage module is used to minimize the effects of the SMH facility in the river reaches
E-16
downstream. It is necessary, therefore, to delineate the spatial and temporal scales of the effects of the
SMH facility on water quantity, sediment transport, and fish habitat. For instance, Schmidt and Wilcock
(2008), in the case of larger dams, considered river reaches as far as 180 miles downstream to test their
proposed indices of geomorphic change. Of paramount importance to the identification of appropriate
spatiotemporal scales are testing and simulation capabilities, which can be used to measure or model
potential effects of the SMH facility in the river continuum.
A limitation of the current analysis is that all of the functional relationships examined in Appendix E.3 are
deterministic in nature. The deterministic nature of these relationships implies that a given input to a
process can have only the specific outcome predicted by the functional relationship. This may be the case
when the process in question is considered in an average sense, but the complexity and randomness in
nature often causes variability in the predicted outcome which is not accounted for by the deterministic
relationship. To address this limitation of the deterministic approach, the functional relationships for the
processes outlined in Appendix E.3 should ultimately be considered from a probabilistic perspective.
F-1
APPENDIX F. FOUNDATION MODULE
A foundation is the element of an architectural structure that connects the structure to the ground and
transfers weight loads from the structure and/or external forces around it to the subsurface. The
foundation module is the structural interface that anchors the generation module and passage modules to
the streambed. It must support the loads of instream modules and the environment, minimize disruptions
to habitat and sediment, and ensure stability for the entire SMH facility. Although the role of the
foundation module within the SMH concept is similar to that of the foundations of conventional
hydropower facilities, a conceptual design of the foundation module herein represents possibly the most
radical departure from conventional hydropower thinking. The need for a foundation module is borne out
of the lack of environmentally compatible, modern methods to safely, reliably, and cost-effectively
anchor generation and passage modules to the stream subsurface. The conventional approach to
hydropower foundation design entails a combination of site specificity and extensive civil works
construction activities: sophisticated field studies to characterize the subsurface; diversion of water to
allow for excavation, leveling, and construction; and the pouring of large quantities of concrete to
produce massive, heavy structures that resist forces imposed upon the facility. Foundation module design
operates under the assumptions that these methods do not achieve efficiency of design, they do not
complement the modular nature of generation and passage modules, and innovation in foundation
methods would accelerate the deployment of SMH facilities.
The other departure that SMH makes from conventional thinking is that full impoundment of a river is not
considered. A large dam that fully obstructs the flow provides stability and resistance, but it does not
represent efficiency of design and it creates a natural barrier that can have negative environmental
implications. New, environmentally compatible methods and technologies are required that provide the
same functionality as traditional dams without the size, cost, immensity, inflexibility, and permanence.
However, a modular approach fundamentally alters how forces are resisted in a structure—conventional
gravity dams have a primary plane of contact between the subsurface and the base of the dam, and the
stresses throughout the body of the structure remain low (FERC 2003). A modular approach will
introduce a new plane of contact between generation/passage modules and the foundation module. The
implications of this configuration must be considered in the design phase.
To economically justify the feasibility of an SMH project, it is necessary to minimize costs associated
with civil works in the foundation module design. For example, the module would need to be designed in
a way that minimizes ground excavation if possible; minimizes disturbances in river connectivity during
installation, operation, and maintenance (e.g., avoids the use of coffer dams where appropriate);
minimizes benthic habitat disturbances by reducing the footprint of the module structure; reduces overall
installation times; facilitates ease of installation; and uses advanced materials rather than concrete. In
some cases, the foundation module may be designed with a simple anchoring system connected to other
module structures without a conventional concrete-type foundation. For example, either a foundation
module or the passage/generation modules may be anchored into the streambed using steel wires or
beams, if the rock or soil foundations have enough bearing capacity to resist weight loads and external
forces. A well-designed foundation module provides stability for other module structures by preventing
slipping, overturning, seepage, uplift, sinking, and excessive sediment deposition and scour for both
normal operating conditions and extreme environmental conditions (e.g., earthquakes and floods) without
a significant impact on the surrounding stream environment.
F-2
F.1 OBJECTIVES
The primary technical objective of the foundation module is to provide stability and support for SMH
infrastructure (e.g., passage and generation modules) by anchoring the foundation module into the
streambed and banks.
To achieve this primary technical objective, the following specific objectives need to be accomplished:
1. Provide structural resistance against imposed loads.
2. Ensure stability of the SMH facility.
3. Minimize the mechanical impacts of moving water and sediment on the streambed.
4. Integrate structurally into generation and passage modules.
A conceptual example of the foundation module design is displayed in Figure 46 and Figure 47. While it
is represented as a black box foundation structure, the foundation module could be a simple anchoring
system that consists of driven piles and a prefabricated box caisson, or it may consist of more complex
structural members.
Figure 46. Conceptual schematic of the imposed loads a foundation module must resist.
Foundation Module Primary Objective
Anchor passage and generation modules to the streambed and banks.
F-3
Figure 47. Conceptual schematic of the environmental mechanics a foundation module must resist.
F.2 REQUIREMENTS
Foundation module requirements further describe the specific objectives an installed module should
achieve (Table 33).
Table 33. Foundation module requirements. In the fourth column: F = Functional; P = Performance; I =
Interaction; O = other. In columns 6–11, an “X” denotes a relationship to the river continuum constituent
indicated in the top row
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Water
Fish
Sed
imen
t
Recrea
tion
Water Q
uality
1
Provide structural
resistance against imposed
loads
F, P, I X X X
a
Resist maximum static
loads from the general and
passage modules
F, P, I
The foundation module (FM)
should be able to bear the
static loads of the generation
and passage modules to
prevent sinking, while the
bearing capacity of the
subsurface must be adequate
to support all modules
X X
F-4
Table 32. Foundation module requirements (continued)
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Recrea
tion
Wa
ter Qu
ality
b
Resist the hydrostatic and
hydrodynamic force of
water, debris and
sediments
F, P
The FM should be able to
bear the dynamic loads due to
hydrostatic and hydrodynamic
force of water, debris, and
sediments to prevent
undercutting, sliding, uplift,
and overturning of the FM
X X X
c
Resist maximum dynamic
environmental loads from
extreme events (i.e.,
earthquakes and floods)
F, P
The FM must be designed to
withstand the instantaneous
and sustained forces imposed
upon it during extreme
conditions for reliability and
public safety
X X X
2 Ensure stability of the
SMH facility X X X X
a
Maintain force and
moment equilibrium
without exceeding the
limits of
passage/generation
module-to-FM, or FM-to-
subsurface strength
F, P, I
When the all forces imposed
upon a structure are in
equilibrium, it achieves
stability. Similarly, the
moments of force must be
sustained to eliminate the
possibility of overturning. The
magnitude and direction of
forces and moments to be
encountered during normal
operation must be considered
to ensure designs resist sliding
and overturning
X X
b Prevent seepage
If the subsurface consists of
pervious sands and gravels,
seepage under the foundation
structure or piping through the
FM will reduce structural
stability
X X
c Prevent uplift
Water seeping through the
FM or subsurface can result in
uplift. Reduction of uplifting
forces can be achieved
through a proper drainage
system, a use of grout curtain,
and by accumulation of low
permeability silt in the
X X
F-5
Table 32. Foundation module requirements (continued)
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Recrea
tion
Wa
ter Qu
ality
upstream side
d Resist erosion or scour of
the surrounding streambed
The energy of water leaving
the generation of passage
modules will impose a load
on the downstream portion of
the FM that could lead to
erosion of foundation
materials over time or
scouring of soils. Erosion and
scour may cause instability of
foundation structure due to
reduced structural integrity
and undercutting of soils,
respectively
X X X X
e
Prevent settling,
subsidence, and downward
migration of the SMH
facility
Conventional dam
foundations and subsurfaces
are extensively scoped for
fissures, caverns, and settling
and subsidence potential.
Foundation treatments,
compaction, and fill are
applied to optimize stability.
A foundation module must
incorporate a high strength
and geotechnically
appropriate interface with the
subsurface and with modules
overhead to minimize settling
and subsidence of the facility.
The installation module will
play a critical role in
identifying subsidence
hazards.
X X X
3
Minimize the mechanical
impacts of moving water
and sediment on the
streambed
X X X X
a Resist scour downstream
F, P
The energy of water leaving
generation or passage
modules may be carried
downstream past the FM,
resulting in scouring of soils
over time. The FM may need
X X X
F-6
Table 32. Foundation module requirements (continued)
Requirement Type
(F/P/I/O) Formalization/rationale E
nerg
y
Wa
ter
Fish
Sed
imen
t
Recrea
tion
Wa
ter Qu
ality
to incorporate energy
dissipation features to reduce
the flow of energy, and
therefore scour
b Resist deposition upstream F, P
Too much sediment deposited
upstream side of the FM
structure as a result of poor
design of modules and/or a
reduction of stream power,
can cause poor water quality,
algal blooms, and habitat
degradation
X X X
c
Prevent turbulent
disruptions of the flow
field
F
Turbulent disruptions of the
flow field, which may be due
to poor design of modules
and/or excessive operation,
should be minimized so as not
to disturb the environment
and to maintain the structural
integrity of the modules
X X X
d Minimize benthic habitat
disturbance F
Benthic habitat disturbance,
which may be caused by
installation of the FM or scour
and/or deposition of
sediments during normal
operation, should be avoided
X X X X X X
4
Integrate structurally into
generation and passage
modules
X X
a
Transmit all forces from
generation and passage
modules into the ground
F, P, I
Passage and generation
modules will be placed
instream on foundation
modules that interface with
the streambed. The integration
between foundation modules
and passage and generation
modules must be strong,
robust, and flexible/scalable
to accommodate different
module sizes.
X
F-7
F.3 INPUTS, FUNCTIONAL RELATIONSHIPS, AND PROCESSES
A good foundation module design should eliminate the possibility of failure from overturning, uplift,
sliding, and tilting that might occur if the forces imposed upon the foundation exceed the module strength
or the bearing capacity of the underlying subsurface. Proper design requires knowledge of the forces,
loads, and combinations thereof that will be imposed on the module in normal operating conditions and
during extreme events, the bearing capacity of the subsurface and the structural rigidity of the module,
and the material properties of the subsurface and the module. Many of the forces imposed on a hydraulic
foundation structure are difficult to quantify with precision; engineering judgment, simulations, and/or
testing are used to estimate the location, intensity, and direction of these forces and their impact on
overall foundation performance.
F.3.1 Necessary Inputs
Table 34 lists necessary inputs for foundation module design.
Table 34. Foundation module necessary inputs for module design
Identification of
key inputs Formalization
Flow variables
Range of flow rates, average hydraulic head, water depth, velocity,
turbulence parameters, friction factor, watershed hydrologic
characteristics, flood frequency and magnitude, inflow design flood
Head Average hydraulic head, hydraulic head at flood conditions
Generation module and passage
module loads
Envelope of loads (static and dynamic) resulting from normal operation of
the generation and passage modules
Geomorphologic variables
River bed slope, bed topography, friction factor, channel sinuosity,
substrates, soil type, depth to bedrock, structure of strata (strength,
thickness, inclination, fracturing, porosity, gradation, angularity, shape,
moisture, shear strength, permeability
Sediment characteristic variables
Sediment grain size distribution (e.g., median grain diameter, geometric
standard deviation), friction factor, sediment fall velocity, sediment
angularity, sediment shape, relative protrusion
Stream cross sectional area Bottom width, wetted perimeter, depth, side slope
Location of potential failure planes The most vulnerable areas where imposed loads will cause modules to
slide along a plane, resulting in module failure
Externally imposed force variables Hydrostatic forces, hydrodynamic force, earth and silt forces, magnitude
of these forces expected to occur during failure
All module dimensions
(foundation, generation, and
passage modules)
Length, width, height
Foundation module construction
material Density, strength, stiffness, porosity, permeability, erodibility
Foundation anchor design Material properties, dimensions, installation method
F-8
F.3.2 Functional Relationships
Table 35 lists functional relationships for foundation module operation and their rationales.
Table 35. Functional relationships governing foundation module operation
Relationship of To Rationale/importance
Static and dynamic
loading of the
foundation module
Bearing pressure
and mechanical
properties of the soil
and subsurface
The bearing pressure of the subsurface is related to the geology,
bed material, topography, and bathymetry, with consideration of
their evolution throughout the life of the project. These features
must be identified and classified for the most common
deployment scenarios, with emphasis placed on both streambeds
and stream banks, to determine viable foundation module (FM)
designs
Static and dynamic
loading of the FM
Strength of
foundation module
materials
The deformation, displacement, vibration, compression, and
material failure characteristics of the FM material must be
understood with respect to the envelope of static and dynamic
loads to be encountered. A relationship predicting the shear
friction within the module and at the modular interface with the
subsurface and other modules is necessary
Module designs
1. Undercutting
2. Uplift
3. Sliding
4. Overturning
5. Benthic habitat
disturbance
6. Scour and
deposition of
sediments
7. Erosion of the
FM
1. Effective design of the FM may prevent undercutting
2. Effective design of the FM (e.g., the use of proper drain
system) may prevent uplift
3. Effective design of the FM will minimize the excessive shear
stresses caused by dead and live loads
4. Effective design of the FM will prevent overturning
5. The footprint of the FM designs may determine the degree of
benthic habitat disturbance
6. Effective design of the FM may prevent excessive scour and
deposition of sediments around the structure
7. Effective design of the FM may prevent the erosion of the
structure
Flow depth
upstream of facility
and FM material
composition
Seepage potential
Seepage under the FM and subsurface erosion must be
considered a possibility at all sites. The use of new and
innovative foundation methods and materials will require new
relationships to identify seepage potential, and the best means to
incorporate seepage mitigation measures into the FM
Generation and
passage module
flow energy
Energy dissipation
requirements
The energy carried by water flow out of the generation and
passage modules may require dissipation by the FM to reduce the
possibility of scour past the downstream end of the FM.
F.4 MEASURES OF PERFORMANCE
The primary foundation module measures of performance are the ability to provide structural resistance
and stability against the imposed static and dynamic loads in a safe and reliable manner (Table 36).
However, these primary performance measures are difficult to gauge in a prototype until the module is
stressed or fatigued to failure. Therefore, structural performance measures must be modeled and/or tested
in a more controlled environment (i.e., a test facility) to ensure that the module design can satisfy all
functional requirements. In addition, module scalability, size of the module, installed cost per module,
estimates of module useful life (durability), and environmental disturbance are additional performance
measures to be qualitatively and/or quantitatively gauged.
F-9
Table 36. Foundation module measures of performance
Index Status
Stability against sliding More research and modeling/testing needed
Strength of foundation module materials More research and modeling/testing needed
Scalability More research needed
Size More research needed – minimize instream and subsurface volume
Cost More research needed – long-term facility target of <$6,000/kW
Environmental disturbance More research needed – deposition and scour minimized
A foundation module should maintain stability during normal and extreme flow conditions, such as a 100-
year flood event. Stability criteria may vary for a particular combination of imposed loads, based on the
knowledge of inter-module interactions and interactions between the foundation module and the site
subsurface. In most conventional dams, stability is achieved by using the weight of a large, heavy
structure to resist the horizontal force of water. Acceptance criteria for the stability of existing gravity
dams are based on factors of safety—the ultimate strength of the foundation materials is divided by a
safety factor to determine the allowable stresses that can be safely sustained under various static and
dynamic loading conditions (FERC 1999). An additional factor of safety characterizes the actual shear
plane resistance, which must be some factor higher than the shear plane resistance that would initiate
sliding. There is generally a large uncertainty associated with this analysis, as the cohesive bond between
the dam structure and the subsurface interface is difficult to quantify. A modular approach does not rely
on a massive gravity structure for stability but instead strives for low-profile, ecological compatibility,
minimized designs that can transmit horizontal loads directly into the subsurface through innovative
means. Additional research, modeling, and testing are necessary to determine the optimal configuration,
inter-module cohesion mechanisms, and foundation module–to-streambed interface that will maximize
stability.
The material properties of the foundation module—most important, the shear and tensile strength of the
materials used—are important to assessing the overall strength and stability of the module. In
conventional small dams, the shear strength along the dam–foundation interface, comprising the friction
angle and cohesion of the material(s) interface, is the most important variable to understand in a stability
analysis (Paxson et al. 2011). These values are well known for conventional dams, but additional
research, modeling, and testing of foundation module designs is necessary to develop acceptable
performance measures.
The foundation module must be designed in such a way that it can be well coupled with various sizes of
other modules to effectively and economically achieve the specific objectives under a range of flow
conditions, head, site topography, and subsurface geology. The foundation module can be assessed based
on the number of modules required to support a given supply of kilowatts, or cubic feet second of flow, or
number of foundation modules per generation or passage module. A building-block style foundation
technology could use precast segments with interlocking elements to provide rapid in-field installation
and removal. A scalable module will need a high-strength interface that can sustain the stresses identified
in the stability analysis; thus more research to quantify the tradeoff between scalability and strength is
necessary. However, module installation, replacement, refurbishment, and administration can be
streamlined and made more cost-effective if a common module can be scaled across multiple sites.
A foundation module should be sized to safely and economically support other modules while remaining
amenable to standard transportation methods and/or ease of fabrication on sites with minimum civil works
construction. An exemplary module will reduce the overall footprint of the SMH facility and minimize
the need for access, dewatering, excavation, leveling, or grading, which will not only reduce costs but
also minimize environmental disruption associated with construction activities. Although this concept is
new in the hydropower industry, the construction industry is rife with innovative environmentally
F-10
compatible and minimal-size designs and techniques. Soil nailing, for example, is a technique used as a
retaining wall alternative for either permanent or temporary construction. Compared with traditional
retaining walls, soil nailing offers multiple advantages, including elimination of excavation and backfill,
reduced material and cost requirements, smaller footprints and right-of-way requirements, and improved
safety. (FHWA 1998).
There is a large degree of uncertainty in setting a specific target installed cost for a foundation module, as
is also the case for other SMH module structures:
A site may consist of a generation module and a foundation module, or it may require several passage
modules and foundation modules. Depending on the settings of the sites, the installed cost of the
foundation module would vary in each case.
The cost to precast, deliver, and install a foundation module may be greater than the cost of existing
construction technologies; but the modular development of a project may reduce civil works and other
project soft costs, improving project feasibility.
The use of innovative methods and advanced materials may further reduce the costs associated with
the foundation module fabrication and installation.
Based on these uncertainties, it is most instructive to set an upper bound on installed cost, under which a
foundation module should strive to fit. The immediate target for an SMH project should be less than
$6,000/kW, including all modules necessary at a site. Over time, this number should be reduced as
module deployment increases.
The degree of environmental disturbance associated with foundation module installation and operation
may be minimized by establishing a strategic design plan. This strategic plan may include a smart design
that can minimize the mechanical impacts of moving water and sediment on the streambed, enabling
minimal scour and deposition or self-cleaning of sediments upstream and downstream. It also may
include an effective design that can minimize the foundation module footprint, which may directly affect
benthic habitats. An index of performance should be established to categorize the installation disturbance
and instream functionality with respect to sediment and scouring associated with a foundation module.
F.5 CONSTRAINTS
Table 37 lists design constraints for foundation module design.
Table 37. Foundation module design constraints
Constraint Formalization
Scale
(L= local,
G = global)
Type of subsurface
Subsurface soil/bedrock characteristics
should be stable enough not to require
extensive treatment. The bearing pressure
exerted by the facility must not exceed the
limiting shear resistance of the subsurface,
and soils that lead to excessive settlement
must be avoided
G
Module must not require extensive
excavation
In combination with limiting the type of
subsurface where a foundation module
should be applied, the excavation needs to
install and sustain a foundation module must
be minimized
G
F-11
Table 38. Foundation module design constraints (continued)
Constraint Formalization
Scale
(L= local,
G = global)
Dewatering of a stream-reach for module
installation is not allowed
Environmentally compatible installation
methods must be used for the foundation
module, meaning a cofferdam or full
dewatering of a given stream cross-section is
not allowed
G
Foundation module (in combination with
passage and generation module) cannot
fully impound a stream-reach
An SMH facility must maintain the flow of
water, energy, sediment, fish, and small
watercraft throughout a stream-reach. This
facility level objective is best achieved by
ensuring the stream-reach is not fully
impounded
G
Unit stresses of foundation module
materials cannot be exceeded under normal
static loading
Foundation module materials with shear and
tensile strengths that sustain the combined
normal and maximum dynamic and static
loads must be used
G
Safety factors
The existing safety factors for low-hazard
dams may not be applicable to modular
foundation structures, although they can
serve as a starting point for estimating the
strength and stability parameters that must be
maintained. They generally relate to usual,
unusual, and extreme loading, and the
probability of occurrence of each condition
G
F.6 DESIGN ENVELOPE SPECIFICATION
A foundation module is necessary to enable the installation of generation and passage modules and to
ensure the success of an SMH facility. This module is perhaps the most unique and most challenging of
the SMH modules. Conventional approaches to hydropower development have relied on massive concrete
structures for stability and support, whereas future SMH facilities will require minimized foundation
designs, materials, and configurations that are strong and stable yet flexible and scalable, and installations
that limit overall environmental disturbance.
It is clear that the environmentally compatible, low-profile, efficient foundation modules described in this
section can be realized only through innovative and superior design strategies. The objectives,
requirements, constraints, and measures of performance outlined represent a first attempt at identifying
the functionalities that designers must target to produce an exemplary foundation module. Given the
variety of potential known and unknown development site characteristics, environmental attributes,
subsurface types, and potential new foundation materials and techniques to be employed, the list is not
exhaustive; and a large degree of uncertainty persists in the module design envelope. The following points
summarize the topic.
The foundation module must resist static and dynamic loads without the use of massive concrete
structures.
High-strength designs are necessary that transmit horizontal loads into the subsurface while
minimizing the use of materials.
F-12
The foundation module must provide stability for the entire SMH facility. Additional research,
modeling, and testing are necessary to characterize how interlocking and scalable foundation modules
can sustain the stresses of operation at modular interfaces.
Environmental disturbance must be minimized through environmentally compatible, low-profile
designs that minimize the need for access, dewatering, excavation, leveling, and grading.
The foundation module must extend upstream and downstream and act to minimize the impact of
sedimentation and scour, respectively.
The use of advanced modeling and testing capabilities is critical to ensuring the success of future SMH
facilities and foundation module configurations.
G-1
APPENDIX G. TERMINOLOGY
The definitions in Appendix G are subject to change.
This report includes references to both new and conventional terminology with respect to small
hydropower. Key terms and concepts, and their respective definitions, are provided below for reference
throughout the report.
Design Constraint: a limitation on the value of a design parameter or a limitation on an effect of
deployment or operation that must be satisfied and verifiable to ensure feasibility of a module or facility.
They are characterized as local when they pertain specifically to an individual module, and global when
their validity can be extended to the other modules of the SMH facility.
Design Specification: the objectives, requirements, constraints, and measures of performance of a
module that developers will need to address in their design.
Environmental Disturbance: disruption to the flow, exchange, or transfer of water, energy, fish and
aquatic species, sediment, and water quality in a river system.
Fit-for-Purpose: a design philosophy intended to produce a solution that is cheap, fast, and meets the
intended need for which it is developed.
Foundation Module (FM): a module situated between the streambed and passage and/or generation
modules dedicated to resisting the forces of operation and supporting or bearing the loads imparted by
modules and the environment.
Functional Analysis: the method of developing and analyzing functional requirements, functional
relationships, constraints, and exemplary characteristics on a module and facility level and determining
how they are accounted for in facility design.
Functional Decomposition: the process of developing and analyzing facility and module objectives,
requirements, functional relationships, constraints, and measures of performance and determining how
they are accounted for in facility design.
Generation Module (GM): a module with dedicated functionality for hydroelectric power generation.
Measure of Performance: a set of quantifiable indices or metrics that enable the evaluation of a module
with respect to how well it accomplishes specific and primary technical objectives.
Modules: an independently operable unit with dedicated functionality from which an SMH facility can be
constructed. Modules discussed in this report have dedicated generation, passage, and foundation
functionalities, and will be described in terms of functional requirements, constraints, and module
characteristics, rather than a discrete physical form. SMH modules are conceptualized to be independently
interchanged to achieve a configuration appropriate for the scale and environmental context of the site
selected for development.
Modular Interface: the mechanism through which a module connects to other modules.
Module Enclosure: the outer surface of a generation module that seals inner equipment and systems.
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Module Standardization: the predictable and scalable development of generation, passage, and
foundation modules. An individual module must incorporate all intended purposes and form a single unit
that reliably interfaces with the same type and other types of modules.
Passage Module (PM): a module with dedicated functionality for the upstream to downstream passage of
water, sediment, recreational craft, and fish, or the downstream to upstream passage of fish.
Primary Objective(s): the ideal goal(s) of an installed and operational module or SMH facility.
Requirement: a feature of a module or facility that (1) is essential to achieving the primary objective, (2)
is verifiable through testing, measurement, or observation, and (3) in combination with other requirements
indicates that the module or facility is achieving its primary objective. They are characterized as
Functional, Performance, Interface and Other, based on the following criteria:
Functional requirement: The requirement is a behavior or function that needs to be performed for
successful module operation.
Performance requirement: The requirement is quantified by how well a function is accomplished.
Interface requirement: The requirement involves interaction of the fish passage module with other
modules, e.g., water passage, generation.
Other: There is a lack of knowledge regarding the requirement at present.
Specific Objective(S): a set of goals or actions that must be accomplished to ensure the primary objective
is achieved.
Stakeholders: a person, entity, business, organization, or agency with an interest in hydropower. Key
stakeholder categories identified in the SMH MYRP include Water Management and Allocation,
Regulatory and Standards Agencies, Resource Managers, Advocacy and Outreach, Standards and
Certification Entities, Electric Utilities, Hydropower Asset Owners, Project Development Interests, and
Technology Developers.
Sub-Modules: a smaller sub-set of a larger module. For example, a generation module may be comprised
of an intake sub-module, a hydraulic chamber and hydraulic water turbine sub-module, an electrical
generator sub-module, and a draft tube sub-module.
H-1
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